Sorry for necroposting, but there seems no googleable solution. Seems I found one. There is vcvars.bat file, which is used for setting correct environment variables for VC. QtCreator, for example, use it while setting Tools -> Options -> Build & Run -> Compilers. Also it is used for MSVC Command Promt. Let`s check "VisualStudioVersion" env var in qmake (14.0 for MSVS 2015 in my case):
win32-msvc* {
MSVC_VER = $$(VisualStudioVersion)
equals(MSVC_VER, 14.0){
message("msvc 2015")
}
}