Bobbiin is OK ..... but, in recent years there has been a lot of variation in the grove that fits over the peg on the winder. Some of the newer bobbins have a groove that's so small it won't engage or stay engaged. Sew-Classic has a big notation on the metal Class 15 bobbins she sells to that effect.
As far as I can tell the peg on your winder looks to be a bit worn, but I can't tell for sure. On my Singers and clones with the peg type winder I pic out bobbins that fit the peg for each machine. My current 15-91 hasn't been used yet, (needs major cleaning and service) but I'll take a pic of the winder later today for you.
Joe