I had Visual Studio 2015 RC installed and basically installed Visual Studio 2015 RTM over it. Couldn't find anything on the internet that said you couldn't do this. Don't know if this is relevant to the problem.
Unfortunatly when I started up VS 2015 RTM for the first time after restarting it popped up messageboxes with:
"The 'Microsoft.VisualStudio.Editor.Implementation.EditorPackage' package did not load correctly"
Also:
XamarinShellPackage
TestWindowPackage
NuGetPackage
ErrorListPackage
It said to look in the ActivityLog.xml. I couldn't find Microsoft.VisualStudio.Editor.Implementation.EditorPackage.
But for XamarinShellPackage it said: