I am running Visual Studio Enterprise 2015 RTM on Windows 8. In Visual Studio 2013 the Build Explorer was in Team Explorer -> Builds -> Actions -> Manage Queue. That option
The links that bring up the Build Explorer (Manage Queue) are gone from VS2015. However, if you double-click any build definition in the Team Explorer list of "XAML Build Definitions", the Build Explorer tab will appear.
Unfortunately, that menu option (and a few others) were removed in 2015. The Visual Studio experience has been refocused on the dev showing just the Builds page. We (the tfs build team) expect build admins and those who own definitions to start on the Web and not really use Visual Studio.
That said, if you still have XAML build definitions, then you are tied to Visual Studio to edit those definitions.
Sorry for the unexpected change in behavior. Jason Prickett