I’m posting here because I think I found a bug. If I am right, please submit a bug report. If I am mistaken then please move this and answer it for me.
If I rebuild the Visual project files from inside the editor, it correctly builds a solution setup for VS 2015.
If I rebuild them from Explorer (by right-clicking on the .uproject file), it builds a solution setup for VS 2013.
I do not have VS 2013 installed, just 2015 and 2010.