VS2015 is safe for now, although I'd not got any further up. Basically, when a new VS version is being released it might take some time, to get special IDE shenanigans back-ported, same goes with new Xcode versions on Mac. If you want to build plugins against official versions of WS, or just want to distribute versions of plugins, which should run with official versions of WS, you have to get the VS2013 route, as otherwise the end-user might run into a dll-linkage hell with the c++ redistributables.
regards
Roland