FH-11W deck should work and use the same wide wire connector plug to the amp/radio section.
I have the TC-118 double cassette deck on my FH-11W and replaced the belts and all once. Everything was working including rec and playback. Later it showed a little lower speed with the play. It was not at all easy to take this twin deck apart. Very time-consuming job! The hardest deck job I did so far!
Now, I am a bit reluctant to go inside it and adjust the motor speed. Now I seriously doubt my skill levels ...
TC-118 or TC-158R decks should work on your 15R.
This is the TC-158R deck your FH-15R uses