Problem with 2015/4.5

I see that there's a fork project that says it's for VS 2015 and .Net 4.6, but I'm on a project using 4.5, and I can't seem to get SpecsFor.MVC working. The regular version fails to install right, complaining that the browser drivers already exist. I can push past that by trying the install multiple times, but I still don't end up with a SpecsFor.Mvc reference in the project, even though the NuGet package seems to think it should be there. I tried the fork project, but didn't have any better luck there since it wants to reference a higher version of the System.Web.Mvc assembly.

Is there anything else I should try?