Guess I'll be the odd woman out. Many of the metal bobbins don't fit the 15 bobbin winder well. Sew Classic doesn't even test the metal ones anymore or recommend them for the 15 because the quality control in China is down the tubes. The best bet is to try and find vintage class 15 bobbins. I don't have issues with the new metal bobbins working in many of my machines, but the 15's bobbin winder is very particular about the correct fit.