It's a 15. Those are the only Singer models to have the tension on the faceplate. If it's got a treadle, it's a 15-89, if it has a belt, it's a 15-90, and if it is gear driven (no belt) it is a 15-91. I have a 15-91 and they will sew through ANYTHING. It's a great machine if you are going to make bags, or anything with thick seams.
Congrats on both.