Singer 15 slow to stop?

I have an old Singer 15 which I was given to me by an elderly friend. When I take my foot off the pedal, it does not stop immediately. It slows down but carries on sewing for 2 or 3 inches depending how fast I am sewing. There is no capacitor in the foot pedal. I had that happen with an old Bernina and I know what it is like. I have searched the internet over and over again and I can't see any information about this fault. I don't know if it is the foot pedal or the motor that is causing it. Any thoughts would be appreciated. Thanks for reading.