Sorry, no MSVC 2015 on hands, just tried with MSVC 2013:
call "C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" x64
nmake -f Makefile.msvc
After that:
mem-image -4 -6 filename.cr2
filename.cr2.ppm (16 bit, linear) was produced, looks OK
Sorry, no MSVC 2015 on hands, just tried with MSVC 2013:
call "C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" x64
nmake -f Makefile.msvc
After that:
mem-image -4 -6 filename.cr2
filename.cr2.ppm (16 bit, linear) was produced, looks OK