Can you advise me as to where the Layout templates I create are located in the file system
C:\Users"Your user name"\AppData\Roaming\SketchUp\SketchUp 2015\LayOut\Templates
Note that the AppData folder is hidden by default so to see it you will have to enable the visibility of hidden files and folders in Folder options.
(Moved to LayOut category.)
See also: Layout Template Location