Hi ,
There are still some updates to the source code that need to be made to make it fully compatible with Visual Studio 2015. This is one of the issues that can occur (VS 2015 defines this differently than VS 2013 does, but from what we can tell there is no actual problem with this change in UE4’s source code). I am hoping to find some time soon to create a list of source code updates that are needed to be able build the Engine using VS 2015.