Nexus 6P Heating Issues
I recently bought a nexus 6p myself and upgraded it to Nougat (Android 7.0).
It burns like a stove after playing 10 minutes of any 3D games (in my case, Walking Dead: No man's land), and that's both before and after the system update.
I think the following article explains the reason pretty well, it's all about the processor:
http://www.androidheadlines.com/2015/10/huawei-nexus-6p-good-bad-ugly.html

I tried wrapping an ice pack with a towel under my phone while using it and it helped a lot.
I'm not sure if that's good idea though because people say that it will definitely cause condensation inside the device and void the warranty.