No Compiler? Visual Studio 2015 is installed

How can I help get 2015 supported? I am a software engineer and would be glad to contribute, plus it will help me get more familiar with how UE works.

I started working on a project I was creating to learn game dev after a few months. I am now on Win 10 from 7, UE 4.9 from 4.7 and VS2015 - VS2013. I can’t open my project, it wants to rebuild. I tried rebuilding it via cli to the 4.9 install dir by adding the -2015 flag but it fails to build a specific file at 25%. I attempted to build via the 4.9 cloned branch, it couldn’t find the unrealheadertool, I copied that from the install dir and it made it to 33% and failed to find scriptgeneratorplugin.