First off, this is kind of a Windows-y (Windows 10) question, but I think the answer will be more AE-specific . . . .
I am running 2014 and 2015 fine on my Windows 10 PC, provided I open them up directly. If I double-click on an .aep file, though, it always opens with 2014, and no matter how many times/ways I tell it to change the default, it always opens 2014.
Is there a way to change this? I suspect it's because both versions have the same .exe file name, but I don't want to go changing file names at that level.