I haven't set up VC14 yet. So far I had no fun to install a second Windows installation on a different hard drive. Installing different VC versions parallel did not work in the past.
Shouldn't be a problem. I am running VC9, VC11 and VC14 (and VC8/10/13), x86 and x64 all on 1 machine. I have got 6 directories with dependencies:
C:\php-sdk\win32build.vc9
C:\php-sdk\win32build.vc11
C:\php-sdk\win32build.vc14
C:\php-sdk\win64build.vc9
C:\php-sdk\win64build.vc11
C:\php-sdk\win64build.vc14
When I open the VC14 x86 prompt I make a symlink in C:\php-sdk\win32build:
rd \php-sdk\win32build
mklink /J \php-sdk\win32build \php-sdk\win32build.vc14
So my dependencies are always in \php-sdk\win32build for x86 and in \php-sdk\win64build for x64. That is where the PHP build process is looking, but for compiling Apache this works equally well.