Crewsemj,
You have a Singer 15-91. If the buttonholer is correct for the box its in, it will work with this machine.
I use a cone thread stand when I have a machine without a spool pin. Here's a link to a manual for a 15-88/89 it'll work just fine.
http://www.sil.si.edu/DigitalCollect.../NMAHTEX/2665/
Sharon W