Just buy a fully specced 2015 15" rMPB. I did and it's amazing. Not one bit slower, because Skylake is energy focussed, bigger battery, better keyboard, useful ports, magsafe etc. etc. etc.
Actually, in practical use, the 2015 MBP IS "one bit slower" (actually, up to about half-fast slower); because the Thermal Management in the 2015 model kinda sucked, and so the CPU and GPU ended up being THROTTLED,
even as low as about 50% speed, when doing CPU or GPU-intensive tasks (like, ya know, when you'd really NEED it!); whereas the improved Thermal Management (and Reduced Power Consumption) in the 2016 model allows the CPU and GPU to cruise along at 100% speed pretty much indefinitely.
Here's an article showing how dramatic the CPU and GPU throttling is in the 2016 MBP:
http://www.notebookcheck.net/Apple-MacBook-Pro-Retina-15-Mid-2015-Review.144402.0.html
Versus the 2016 MBP, which apparently exhibits NO throttling. Check out this EXCELLENT, highly-detailed, review of the 2016 MBP. Throttling (or lack thereof) is mentioned in a couple of places, and there is an extensive "Temperature" section of the review:
http://www.notebookcheck.net/Apple-MacBook-Pro-15-Late-2016-2-6-GHz-i7-Notebook-Review.185254.0.html
Same thing for the Battery: As pointed out in the Review above, smaller battery is offset by the less-power-hungry CPU and dGPU. You see, it's a SYSTEM. ALL the parts matter.
And as for the "useless" Ports on the 2016 MBP: As I have preached long and hard, those FOUR USB-C/TB3 Ports on the 2016 MBP, with their industry-leading, and whopping, 80 Gbps of raw, Multifunctional I/O capability, ARE useful NOW, and will be appreciated more and more during the time you have the Laptop; whereas the dedicated ports on the 2015 model will do nothing but become less and less useful as the days go by. You DO plan on keeping your new Laptop for longer than a year, right? If the answer to that is "yes", then USB-C/TB3 is the ONLY way to go. That's why there are literally DOZENS of
non-Apple laptops with that EXACT same Port.
http://www.ultrabookreview.com/10579-laptops-thunderbolt-3/
Don't be fooled by the I/O Luddites! A little adapter shuffling now is minimal AND temporary. See the picture below. Do you REALLY think that THIS is going to be a major annoyance? Do you REALLY think that the little thingy below it is worth basing your ENTIRE Laptop-purchasing decision on? Stick it on the end of your USB-A cable and FORGET it! Carry a couple of spares if you're afraid. They're like $2.50 apiece. Oh, and they have Micro-USB versions, too that are the same price and look the same as the USB-A ones, if you have devices that have THAT horrible excuse for a connector...
Here's a 3-pack of those adapters for $7 on Amazon. That actually works out to LESS than $2.50 apiece:
https://www.amazon.com/Adapter-Hi-speed-Devices-MacBook-ChromeBook/dp/B01LHBFCEO/
Similarly, this is one place where I differ quite a bit from the review from notebookcheck.net, above. Amazon has SCADS of USB-C adapters and "mini-docks" that are available in a wide-array of port configurations and assortments from around $2.50 to $45 (but the $45 one has everything but FW 800 (USB 3.0, Gigabit Ethernet, 4k HDMI AND 1080p VGA, and STILL only takes up ONE USB-C Port). You can also get a mini-dock that has 3 USB 3.0 ports and Gig Ethernet for $22, etc, etc. The point being, with only one or two ports consumed, you can have pretty much any "legacy" ports you need. And when you are ready to replace those legacy devices, the 2016 MBP is Ready.
Remember, you can turn on USB-C/TB3 port into FOUR full-speed (not shared-bandwidth like with a Hub) 5 Gbps USB 3.0 ports; but there is NO WAY to turn a USB 3.0 port into even ONE full-speed USB 3.1 port, let alone a TB 3 or HDMI Port...
https://www.amazon.com/dp/B01C316EIK/
https://www.amazon.com/CableCreation-Gigabit-Ethernet-Adapter-Macbook/dp/B0179UEXOW/
And although pricey, the OWC TB 3 Dock's THIRTEEN I/O Ports clearly shows just how much I/O you can extract from just ONE USB-C/TB 3 Port:
http://blog.macsales.com/38562-owc-...-3-dock-with-13-ports-available-for-pre-order
Mag-Safe: I got nothing. Oh wait! A little pricey; but it does fill the need...
https://www.amazon.com/Griffin-BreakSafe-Magnetic-Breakaway-Chromebook/dp/B01CQTK6GU