I am wondering if you have the right foot. 'For the singer 15 I use a low shank darning foot. You can get this at
sewclassic.com for 3.99. I absouletly love free motion on my singer 15! I love my singer 15's. They are my go to machines. If your starting out FM, the best advice I was given is to practice on felt. It worked great!

I did my foot like Leah Days. Works great. I cut the plastic part so I could see better. And I didnt use a hair band, I used a sliver of wood the thickness I needed and wired in place. And I bent the bar so it doesn't "hop" anymore. Then My sister brought me her foot to break. My kid freaked when Sis said to break her foot. Don't you just love young'uns?

wow that looks like my foot only I put a hair band around the top right under the wire thing that goes over the needle screw...if I didn't have the hair band on it the foot was right on the machine bed when the pressure foot was down.. with the hair band on it there is room to move the fabric around. otherwise the pressure foot is right on the fabric and it will not move..I must be doing something wrong as I called the man I got the feet from and he said they were the right ones for my machine..thanks

When the needle is down, the foot should sit on the bed. When the needle is up, as long as the horizontal piece of wire is on top of the needle clamp, it will raise up lots to be able to move the fabric around. The fabric needs to be "tight" to the bed when the needle is down and while the needle is coming out of the fabric or it will skip stitches and you don't move the fabric when the needle's in it anyway.

I did do the modification that Leah Day shows and the noise difference is amazing! I did it to my Juki and I went from hating the noise to not minding it at all. DH told me once that he could hear when I was stitching from outside. He couldn't anymore once I did the modification.