After installing and then repairing my VS2015 instance I still cannot get intellisense (server side) to work in my MVC views. I get alerted by message promp
The /ResetUserData
solution is your best bet, but I also think I have found out a possible cause of this...
I am currently using Umbraco to create Macro Partials in the BackOffice. When these files get created I click on the Hide/Show all files button to show the Macro Partial in my solution and the Razor Syntax Highlighting seems to stop working so my guess is new files introduced into your solution that aren't created directly through VS cause this issue.
Even when adding the files to the solution the Syntax Highlighting doesn't work.