Let's see, I've got one like that, one like that with the silver, the same vintage with the separate motor (15-90) and then a couple of earlier 15's
BTW - Singer started making this version of the 15 in 1932. The very earliest has a Silver emblem.
15-88 is outfitted with a hand crank
15-89 is the same machine fitted for treadle
15-90 is the same with a solid hand wheel and electric motor with belt
15-91 is the same machine with a modified casting and potted motor.
Most of the 15-XX machines are industrial - so sometimes people get mixed up and think all of them are industrial, but the most common you'll find are lighter made ones (comparatively) for domestic use. It's Singer's longest running model (with variations)
The first came out before 1900, and the last . . . well, they are still making them in foreign Singer factories, mostly hand crank and treadle for markets without electricity. And they look very similar in shape, but aren't as robust.
They are wonderful for sewing and FMQ -
This is my "silver"
And one in a case - btw, the cabinet the Bernina is sitting on in the background is the same style as the one in the OP
Here is a much older 15-31 on the right, with the visually similar 115 on the left. They look the same on the top, but are quite different below - the 115 is a full rotary machine.
This is one of my most recent finds - the 15-31 with the much less common RAF decal pattern,
And for fun - the later version, 15-75
I'm still looking for a very early version of the 15.