Thank you for your post.
That is quite weird. May I ask you for the screenshot? We've seen this issue when people confused installer for some version of VS with another version of VS, but from what you are explaining you got the correct one. The other thing that comes to mind, but it's not likely would be corrupted VS registry so installer would really think there isn't any VS2015.
Please with the screenshot provide us with what version of PHP Tools are you trying to install and exact version of VS2015.