This should work and I have no clue why it doesn't, literally all I am doing is creating a new ASP.NET MVC Web application in VS15 Community, and then I replace the existing min.css file with another one (from bootswatch). And it doesn't change anything.
I have practiced mvc for a bit and every time I tried to change my layout later on in the project, it worked every time, but now as I just decided to get it out of the way straight up it just doesn't do anything.
You'll want to change the non-minified version as well.
Edit: Because the minified version is used when you publish and the non-minified version is used during debug, generally.