The girl on the phone was right. It's the reproduction model 15 that Singer authorized. It's a real Singer, just not an original model 15. Usually when I see them for sale they're listed as "antique" which they're not and the seller usually wants a completely ridiculous amount of money. The feed dog knob on the bed is a give-away. The real model 15s never had one and real 15s with perfect sphinx decals aren't common.
You did well at $5.00 IMO
Congrats on your new machine.
Rodney