That's the model number 15J. I assume it's the same as the later 15, like the 15-90 or -91, but treadle and spoked hand wheel in stead of motor parts. The only odd thing I can see is the small horizontal metal bit in the front, just next to the face plate. I think the JD serial number records might be lost, but there is some info on
this page. It looks like JD numbers were made from 1954-61. It's a late treadle version, it looks all orginal.