I had some help building the libs for windows ( I'm not a big windows user ). @prisonerjohn ( https://github.com/prisonerjohn ) and https://github.com/kentaroid compiled the libs for vs2012. I can reach out to them.
In the mean time you should be able to include the bullet source files in your vs2015 project without the need to compile a static lib. You will need to download them from the bullet git repo.
