I was perusing the estate sales for this weekend and saw this machine. It kind of looks like a 15, as the tension is on the faceplate. If it's a 15, it has to be an early one.
bkay
Yes it's a 15. The earliest ones were treadles. Beautiful 'gingerbread' decals! It should clean up nicely but make sure the wiring is still safe (no exposed or frayed wires.)
It could also be a 115. It has a different type bobbin otherwise looks just like a 15. If that is your machine you'll have to get used to putting thread through a thread guide on the bobbin case.