There have been a few patches to vim's master branch that ensure Vim builds in Visual Studio 2015. Visual Studio has a free "Community" edition that was introduced last year, and one of the main reasons people are excited about the 2015 RC is Microsoft's continued efforts to support cross-platform development.
I'm not really a Windows developer, but I'd prefer to be able to build Vim in Visual Studio rather than having to install GCC for Windows. Builds initially failed under the 2015 RC, but it looks like the main issue was fairly minor. If you're trying out a free RC you should at least be able to get Vim to build again now.