Not St John's Newfoundland. St Jean Quebec. Or more accurately
Saint Jean sur Richelieu
http://wikimapia.org/8051938/Singer-...-Machine-Plant
1 way to confirm the date:
mysingerstory.com - at the bottom of the page. It's been known to be wrong though, so take that with a grain of salt. It has the same information usually as here:
http://www.singerco.com/support/mach.../double-letter - 1954
Normally I would also link you to the ismacs.net site, but it doesn't have anything for the JD numbers.
Model 15s are pretty much the same. If it's a 15K or a 15, or a 15J, it will work the same, any manual should work.
It looks like a 15-90 (has a motor with a belt), and has perhaps the most common decal set I've seen around here (Alberta)
Value is what someone will pay for it. It differs from place to place. It's not a gold mine though. Model 15s are possibly the most plentiful of any machine Singer ever made. The model started in the 1800s, and continue on to this day (though they look a little different.)