Happy to chime in here.Same types. But the bezel / case / back aren't interchangeables from a "/1" to a regular.
Edit: the real name for your watch is "Specialist Series - 1500 GMT".
The 1991 TAG Heuer Dealer Catalog and Price List refers to this watch as Specialist - GMT. I have never seen the terms 1500 and GMT used together in any TAG literature.
The case & most of the dial design are virtually identical to the 1500 Oversize, though.