Hi ErgoAsh,
Just a quick update. I was able to put together a list of the additional updates needed in the source code in order to build the Engine using Visual Studio 2015. I updated the forum thread that was talking about this topic, and I will try to get that list over to this post as well (it may take me a few minutes to get the formatting all sorted out). Keep in mind that I was able to build the Engine successfully, but it did take a few build attempts. It isn’t a simple process, but it does appear to work.
The resulting Engine should run the Editor, but I would not recommend doing any game project work in this Engine. The main reason for that is because projects built in version 4.9.1 (and now 4.9.2 that came out yesterday) still use the VS 2013 toolchain, and will still do so even if the Engine is built using VS 2015. This will most likely cause you to experience some additional problems. I have not yet found the necessary changes to make projects use VS 2015 as well.
One last thing I would like to mention. The Master branch was fully converted to use VS 2015 by default on Tuesday, and it falls back to use VS 2013 if VS 2015 is not installed. That means that projects created in the Master branch will now use VS 2015. However, the Master branch is a live branch (new commits go into it constantly) and does not receive any testing, so I do not recommend using this for active game project development either.