I don't know. The machine has been messed with before I got it. Nothing was right on it. Needle bar was too low, presser foot shaft too high, the two hit each other. Feed dogs were hitting the back of the needle plate. This poor machine is all messed up.
So I'm going to start by undoing the two screws that secure the top shaft parts then turn the crank 180º so it matches the 15-91.
Then we'll see what happens.
Joee