I understand it may not be possible but have you tried with a more recent version of VS?
Its been a long time since I used VS2015 for OpenCV (last version was 3.3), have you tried installing windows SDK 8.1 as well?
Probably a stupid question but did you install the C++ components when you installed VS?
If possible can you post the input to CMake, and the build config which it outputs before you build.