I can neither confirm nor deny, but I believe it is close to a class 15. I think it is slightly smaller but don't know if it is in height or diameter. I also think that it does not have a notch like a 15. I'm wondering if the 15J would work?
From my understanding, this machine was made by Portman and there are other machines like yours,
Good luck getting the machine back in service.
Janey - Neat people never make the exciting discoveries I do.