Rejuvenating a 2015 5K iMac

[seveej]

How to rejuvenate a Late 2015 5K iMac?
Dumb question, I know, but before spending more of my hard earned money, I'd like some peer support.

I'm the kind of person who likes to have screen real estate. I also have old eyes (even though I'm only a 40-something), which means that the 5K iMac is my weapon of choice. I am insanely happy with it, except:
- my Late 2015 CTO (4Ghz i7, Radeon R9 M395X, 2,12 Gt Fusion, 24 GB RAM) is lately having temperature issues. As my local mac service (no Apple stores over here) quoted me a basically ludicrous price for de-dusting the thing, I told them to take a hike and ordered the requisite parts (tools, replacement adhesives) from iFixit. They've arrived, but I have not yet found the time to do the procedure.
- it's not the first Mac I've torn apart, but the first adhesive-using iMac. I've read enough and feel reasonably confident, and was planning to NOT use the adhesive strips until I aim to sell the machine (which might be never) - instead just fixing the screen in place with some adhesive tape on the outside to allow easy future access. This also opens up the opportunity to do some rejuvenating.
- I've become painfully aware that my darling iMac is not exactly young and frisky anymore. OTOH, there's no way I can afford a newer machine (with a big screen).
- Therefore, I'm looking at cost-effective ways to rejuvenate the 5K iMac.
And for that, I'd like your input. My options are (as I see it, but if I've missed something, you're welcome to point it out):
- - boost RAM. Even though I'm a fairly heavy user of Adobe software, I rarely max out the RAM (or come even close). Therefore the upgrade prices (24->32 GB ≈80 €; 24->48 ≈ 280 €) seem a bit steep. Is there any point in going beyond 24 Gigs RAM?
- - increase HDD capacity. I work with photos that come in at 50 megs a pop, so I've been forced to shift my archive onto an external HDD, but I rarely use that (so being able to re-internalize those is not a performance boost). The big question therefore is whether 2021 HDD's are in any significant way faster than a 2015 HDD?
- - replace HDD with SSD. I guess this would potentially make a difference (speed-wise), but as that SSD would be limited by SATA3 (and >2 TB SSD's don't come cheap), can you expect a significant performance boost by replacing the HDD-part of a fusion drive with a SATA SSD?
- - Swap the Blade SSD. I've browsed the discussion here on iMac 27" SSD upgrades, and it seems my system is one of the last where one can expect hiccups. Then again, with post 2015 systems becoming increasingly dominant, I'm not sure that discussion is entirely up-to-date (especially regarding changes brought by latest bootROMs and OS versions), so I honestly do not know how to interpret the situation (I'm adding detailed specs to the bottom of this post in case there's a real genius here). Swinging the price of an adapter and a significantly larger M2 blade would seem like a no-brainer, if success can be assumed as likely. Would increasing the size of the SSD be the most cost-effective option?
- - Finally, is there a fourth option I have not considered?

TIA,

Details: I'm in the EU, and in an area where customs' idea of service is Soviet-style. Prices above are therefore based on locally (or within EU) sourced components.
BootROM version: 447.40.12.0.0
Current OS 10.15.7
Current SSD/HDD: Original, meaning APPLE SSD SM0128G and APPLE HDD ST2000DM001

 

[Nguyen Duc Hieu]

For your configuration & I would suggest the following:

1. RAM upgrade:
I guess your current RAM config is 2x8GB + 2x4GB.
You can try to replace the 4GB sticks with 16GB sticks. 50~60EUR each

2. HDD
HDD in 2021 is slightly faster than HDD in 2015 (near 200MB/s), but no where near the speed of SATA SSD (500MB/s)
So you can think of replacing the HDD with a 2TB SSD (200EUR)
Remember to back-up everything and De-Fusion the drive first.

3. And while you are at it, you can try to upgrade the nVME blade to the highest capacity you can afford.
On price vs performance aspect, I would just get the 500GB blade. (50~70EUR, do not get the Gen4 nVME - expensive one but might not be compatible)

If money is less importance than the hassle to open the machine in the future, just get a 2TB blade.

However, despite of whatever upgrades you might do, browsing through a vast library of photos is often sluggish.

 

[wilberforce]

I used to have a 2014 27" iMac, and now have a 2020 27" iMac. A couple of things to try before opening your iMac:

1. Vacuum along the slots at the bottom with a flat nozzle. Do this with the machine OFF. There is a screen/grate about an inch above the bottom slots that gets clogged with dust. Usually easily removed by vacuuming.

2. Boot from and use an external SSD connected to one of the thunderbolt ports, instead of the Fusion drive.

24GB RAM should be fine. That is what I had. More than 24GB RAM will likely make negligible difference in speed for normal day-to-day tasks. The main difference is I had a 1TB internal SSD. No complaints with speed. However you decide to do it, definitely get rid of the Fusion drive and use an SSD instead, internal or external.

How are the edges of your screen? 2015 iMacs are notorious for pink discoloration and image persistence (not burn-in) at edges. This is basically a cosmetic issue, but may affect your decision on how much to spend on it.

 

[seveej]

I used to have a 2014 27" iMac, and now have a 2020 27" iMac. A couple of things to try before opening your iMac:

1. Vacuum along the slots at the bottom with a flat nozzle. Do this with the machine OFF. There is a screen/grate about an inch above the bottom slots that gets clogged with dust. Usually easily removed by vacuuming.

2. Boot from and use an external SSD connected to one of the thunderbolt ports, instead of the Fusion drive.

24GB RAM should be fine. That is what I had. More than 24GB RAM will likely make negligible difference in speed for normal day-to-day tasks. The main difference is I had a 1TB internal SSD. No complaints with speed. However you decide to do it, definitely get rid of the Fusion drive and use an SSD instead, internal or external.

How are the edges of your screen? 2015 iMacs are notorious for pink discoloration and image persistence (not burn-in) at edges. This is basically a cosmetic issue, but may affect your decision on how much to spend on it.

Thanks I'll try the vacuuming, although I suspect that at least part of my heat issue is dust deeper in the system as well as dried out thermal transfer compounds.

I wish I had bought an TB2 enclosure when they were still available, because now they're starting to be increasingly hard to come by.

The LCD edges? The pink is there, but it's not as bad as in many pictures I have seen, and the persistence issue is also there. And you're right in that it's mostly cosmetic, and as it only affects the 1,5-2 centimeters around the rim, it does not even trouble me when working with photos. But it is likely to affect resale value (should I ever go there) and it does somewhat lessen my enthusiasm for throwing money at the machine.

 

[seveej]

For your configuration & I would suggest the following:

1. RAM upgrade:
I guess your current RAM config is 2x8GB + 2x4GB.
You can try to replace the 4GB sticks with 16GB sticks. 50~60EUR each

I would dearly like to know where that price info comes from. The cheapest PC3-14900 16GB ram sticks I could find in the EU would set me back about 140€ apiece.

 

[Nguyen Duc Hieu]

I would dearly like to know where that price info comes from. The cheapest PC3-14900 16GB ram sticks I could find in the EU would set me back about 140€ apiece.

I'm in Vietnam, not as cheap as China, but cheap enough.
Spend extra money for high speed RAM is not my style. PC3-12800 is good enough.
Spend extra money for new ram is not my style either.
16GB stick is quite rare, but still available sometimes.