Just in case you haven’t noticed it, the NuGet package for Microsoft.VSSDK.BuildTools 15.0 is no longer Preview or Release Candidate (RC, RC2 or RC3) but final release:

As you can see, it has been a long way of previews / RCs to reach this point:

So, it’s time to update that NuGet package and rebuild. Microsoft hasn’t announced yet the release date of the final version of Visual Studio 2017 but it seems that we are approaching that date, at least from the Visual Studio Extensibility point of view. Update (Feb 10): the launch date has been announced for March 7. If you haven’t updated your extension to support VS 2017 yet, the clock is ticking. Here you have the guidance to do it.