I found a copy of the 15-96/98 manual on the Smithsonian site and it's clearly the same machine as ours - same stitch length selector and same decals on the arm of the machine. Learn something new every day - and all this time, I thought it was a 15-30!
It's curious, though, that Singer would have made the 15-96/98, then later, they went backwards in numbers while adding features to the machine. (15-88/89/90/91) Not as nonsensical as Kenmore numbering, just a little quirky. :)
Have you oiled it up and sewed with it yet? Sometimes, it takes very little to get these old gals sewing again. And they sound so happy when you put them back to work! :mrgreen: You have a real treasure, there!