Disable update notification for Flash Player 15.x and newer

Dear all

We run a Citrix Environment (on Windows 2008 R2) and we have our monthly update window. Users complain that they get update notifications for Flash Player when a new version is available but they cannot install the update since they have no permissions to install or update any software on our locked down Citrix environment.We tried already all availabe guides regarding "disable update notification for Flash Player" but no guide seems to work with the latest Version 15.x.  

Which registry key's oder files do we have to modify with what values to finally disable update notifications for Flash Player.

Thanks a lot for your help!