This might seem like a stupid question but I just installed VS 2015 RC and I cannot for the life of me figure out how I'm supposed to get the latest version from Team Foundation Server now. It seems the option has been removed from all right-mouse context menus, including Check in... and all other other TFS related menu items.
You can resolve the issue by running a repair on Visual Studio 2015 (via Add or remove Programs). I had the same TFS menu problems as the original poster as well as 'Chinese' characters in many of my popup menus (in Tools>Options).
Microsoft mentioned on the feedback site that running a repair fixes this and it indeed does seem to work - even though it's a bit daft to have to run a repair minutes after an installation. The repair must do something to clean up those old pieces that the installation doesn't do.