here are a few more, they have have been posted before, but I'll re-do them here for those who haven't seen them. They will work on all low shank machines so they should do ok on my new to me 15-91's!
http://www.quiltingboard.com/t-116176-1.htm
Charlee, thanks for the info about needing to use the cover with the zig-zagger, no wonder it didn't work at all!!
I also have a picot-edger somewhere I gotta dig up and play with.