I found the source
http://www.sewalot.com/dating_singer...ial_number.htm but I'm not sure if a 15K would by Kilbowie, Clydesbank, Scotland or Elizabethport, NJ. I'm thinking that since it's here in MN it's probably a Jersey Girl. Elizabethport was Singer's largest US factory. If anyone has any better information on where machines were made, I'd love to learn about it.