Xamarin Forms is broken on Visual Studio 15 for Xamarin 3.0+

Have a project uses Xamarin.Forms 2.3+ with Xamarin Android Support Nuget 2.3+, and tries to update to Xamarin.Forms 3.0, the Visual Studio 15 complain about MSBuild, then I tried to update to Xamarin.Forms 2.5 by deleting whole project and redownload the source code.

With Xamarin.Forms 2.5, Android support Nuget is unable to update due to "Unable to resolve dependencies. 'Xamarin.Android.Support.Design 27.0.2' is not compatible with 'Xamarin.Forms 3.0.0.482510 constraint: Xamarin.Android.Support.Design (= 23.3.0)'." but clearly I have installed 2.5.1.52, and not 3.0. Why does it complain about 3.0?

Are we getting forced to buy Visual Studio 17 to update now?
(Note: I have tried doing this on an existing machine for Xamarin and a clean machine, with the same result.)