Originally Posted by Mickey2

You can roughly assume it's an early Japanese clone because of the black paint and gold decals, and there's no knob or lever on the base for dropping the feed dogs. I have read some early clones have simaco part numbers stamped on some of the cast iron parts under the base. I would guess very early 1950s if I had nothing else to go on. Later version had small features added like buttons or turn knob for the feed dogs, hinged bobbin cover, various colors; they were reasonably common well into the 1960s.

I'm not sure when the Japanese started making 15 clones, but I guess it could have been as early as 1920s or 1935. By then model 15 for a long time had been improved upon and slightly reworked by European sewing machine factories. The stitch length lever was first introduced on Singer model 15s around 1930. Singer estabilshed a factory in Japan in 1954 if I have the info correct. I'm not sure when the import of Japanese machines became common in the US, but it was some time after WWII.