Don't know about 15K80 but my wife's elederly Singer 328K did the same thing this week. I removed the capacitor and enabled her to finish her task.
Capacitor has written on it:-
HUNTS
Cap. 0-1uF
250v A.C. Wkg
M.P
WA 71 1AI
Assume that's 0.1 micro Farad
According to earlier post the machine can run without it!
http://www.howtomendit.com/answers.php?id=178400
Nick Dyson
February 2010