I have a 15-88 and all I use are the multi-hole class 15 bobbins. I did have trouble winding bobbins until I fine-tuned the bobbin winder. I still have to put a bit of finger pressure on the winder while it's running. The 15-91 balance wheel is a bit different from the 15-88 so I won't tell you how to release your bobbin winder, but it's a step I must make on the 15-88.