Well, worked this weekend on getting  Xamarin for Visual Studio 2015 working.

A few notes:

1. Download installer from Xamarin, but do not run it directly.
2. Kill any Java Exe processes before running installer
3. Locate Installer and RUN AS ADMIN
4. If you get an error at the end of the install process about certain SDK’s not installing.
   1. Go to:  “C:\Program Files (x86)\Android\android-sdk\SDK Manager.exe” and run as admin.
   2. Deselect everything and then select ONLY the SKD’s you need and nothing extra.
   3. Reboot after install
5. Run visual studio in admin mode.
6. Do the follow to create a super simple test so you can debug any other configuration issue.  https://developer.xamarin.com/guides/android/getting_started/hello,android/hello,android_quickstart/

The end result: