GPU on the 15" 2015 model

Only the 2.5GHz model and up have a dual GPU setup, which also includes 2GB of dedicated VRAM for exclusive use by the AMD Radeon R9 M370X high performance GPU so it doesn't have to be fighting the CPU for more. While the new integrated Intel Iris Pro 5200 that comes with all the models is an improvement over the old Intel HD Graphics 3000 that came in the Late '11 MBP (I have one too, am in the process of moving over to a Mid'15 15" 2.5GHz MBP), it won't knock anyone's socks off and suffers from the same shared-VRAM issues all the single-GPU models have. At least all 15" models get 16GB RAM, important in these newfangled sealed no-upgradeables-inside models.

For that same reason if you plan on remaining on the Mac platform, best to kill the piggy bank and get the biggest model you can, cause it is all you will get till the end of its days. No more putting in a bigger HDD, adding more RAM, etc. (I bumped mine up from the default 4GB to 16GB). Also since any "service" usually involves replacing the whole thing, do consider getting AppleCare to extend warranty to 3 years. Don't need to purchase it outright with the Mac, but needs to be purchased and activated within the base 1-year warranty period. See here: http://www.apple.com/shop/product/MD012LL/A/applecare-protection-plan-for-macboo k-pro

Edit: an idea… Install Cody Krieger's gfxCardStatus on your '11 Mac and use it to force Integrated-only GPU operation. Use that to test your games. If they don't run OK there, they probably won't run well on the single-GPU '15 model either.