The 15 is a great machine. I placed one of mine with my friend and periodically service it for her. She was having problems with slow running that I didn't have. We dumped a pile of sand and dirt out of the controller. Oops! I forgot to service that. I recommend everyone ditch their old rheostat controllers and go to the new solid state controllers. It has speeded up my vintage machines and now I am getting a new one for all my old black Singers. They cost $17 or under from Sew-Classic.com. Best money I ever spent. Dirt can't get inside them and if you need new wires too, they can wire them for you for a very nominal price. My 15, 201 301, 221s, 305 all have one now. The 15 is a very forgiving machine, as previously stated. The vertical bobbin can be a challenge for arthritic hands, but great for free motion quilting. Be sure to invest in an LED light bulb, also at Sew-Classic.com, so you won't burn your hands when sewing/quilting. That is also worthy because it will give 3-4 times the clear, white light. You should see the difference. My old eyes are very grateful. Happy sewing.
Donna