Oh Mary, you did good! I have 2 15-91s, 1 at my cabin, and I just bought another one last week for the winter place. I'm looking for a 3rd one because my SIL wants one. Why???? FMQ!! It's great. It's the only vintage singer that I've found that you can drop the feed dogs. And, it does a better job of FMQ than the fancy expensive Viking I have. My DH ask me the other day if I ever use that machine anymore.... I don't use it much. I like the vintage machines so well.
Print yourself a manual off ismacs.com and it will show you how to drop feed dogs. There is a small screw under the machine, near the front slide plate that you turn and it will lower those dogs. If you want to sew again, just turn that screw again and the dogs go back up.
I bought a darning foot from sewclassic.com that works great. I did have to take the thread cutter off the presser bar.... it just slides off... well, I had to wiggle it off. And after cleaning everything and oiling the machine, I adjusted the tension for FMQ and quilted ..... it was that easy. I plan to leave it set up for FMQ and use my other vintage machines for piecing and other sewing. I might set one up with a walking foot for straight quilting. It's so much easier to have several machines set up rather than having to change the foot for every little thing I have to do.
And, you're going to love having it in a cabinet. When you're quilting a large quilt, the machine doesn't scoot all over the place. So, clean it up and have some fun. You know we're all going to want to see what you make with it. I'm so excited for you.... can you tell?