If you mean which versions of MKL would have been tested by Intel with VS2015, the MKL 11.2 update 3 which is released with C++ and Fortran 2015xe updates 3 and 4 would be the production version which should have been tested. I don't know the extent of MKL testing against the Microsoft compiler. It seems only the installer changed from update 3 to 4 to introduce VS2015 compatibility.
If you don't have an urgent reason for moving from VS2013 to VS2015, there may be no reason to rush. Updates of Intel tools are due by end of September.