Cindy,
What's it worth ..... well, take the top off and look at the gears and or mechanics. It should be all steel inside. Clean it up and service it, then sew with it. Then I'll bet you can answer your question by yourself.
I "think" the 15-91 will fit, but to be sure measure from center to center of the hinge pins on the cabinet, and the holes on the 15-91. If they are the same, it'll fit.
Besides, it was given to you, so no matter what someone else thinks it's worth, you're ahead of the game.
Joe