Yesterday repaved my machine and installed Windows 10 and Visual Studio 2015, I then loaded one of the projects I’m working on and I’ve a been shocked to discover that none of my views was rendering in Blend 2015 because of this error: “Cannot add additional fields to a type that does not have a constructor”
Thanks to Blend team I was pointed to a workaround that fixed it (at least for me)
Go to Tools->Options->XAML designer and check the option: Run project code in XAML Designer (if supported) and reload the project
Hope it helps.