Issues with Lightroom 5 and 8GB RAM?

I got my refurbished entry level 2012 15" rMBP in June and I've loved it so far, it's so powerful and the screen is amazing. However, I consider myself a hobbiest photographer and so use Lightroom 5 to process all of my photographs. I've been doing some heavy editing recently in Lightroom and started to notice my laptop slowing down. It mainly shows, for anyone familiar with Lightroom, when I do local adjustments on images. I can paint over an area and it take 2-3 seconds to catch up and re-render the image. Then sometimes when I'm just scrolling through images, photos will render as a mass of massive, pixelated squares which aren't fixed until I force the photo to re-render but zooming into it e.t.c.

I presumed the issue was related to RAM as I only have 8GB so I installed a RAM cleaner which has a built in monitor. Whilst using Lighroom and doing these sort of tasks, my available RAM drops to between 2GB and 1GB, occasionally dropping below 1000mb. I presume this means you don't have to run out of RAM entirely for your computer to start struggling - presumably because it can't request enough RAM.

I'm turning to MacRumors for confirmation that this is a RAM issue, which I obviously can't physically do anything about with a rMBP but if there's something I can do to alleviate the issues I'm having.

 

It's quite a basic free Mac app called Memory Clean. It gives you a bar chart which shows Active, wired, inactive and free memory in numerical values. It also puts your available memory value in the menu bar so you can see it when you're in apps.

 

I only got the app for the memory monitoring side of it. Just so I could actually see how much RAM I was eating in real time. What would you recommend for trouble shooting?

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It labels available memory as 'free memory', so I'm guessing that doesn't include inactive memory.

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There's no unusual delay with spot fixes, I'm talking about when you paint over an area of the picture and it applies certain adjustments purely to that part of the image.

 

I have Camera Raw cache set above 10GB so that shouldn't be causing an issue. I've also never had XMP writing on. I think this is purely a RAM issue and a sign that I run out of RAM easily and Lightroom cannot request as much as it'd like to. This is fine, but since I'm not in a position to buy a new laptop anytime soon it's something I'll have to live with and remember next time I'm in the computer market.