The 115 is a true rotary. It looks just like the 15 but has a smaller hook assembly. I don't think they were made as long as the 15s.
It might be a good idea to keep all your posts about this machine in the same thread. Keeping everything in the same place makes a difference later to those who are trying to find info on a particular machine.
It's a rule on another forum that I like and it works pretty well there.
I forgot to mention earlier that I like the base. Is it staying with the machine?
Rodney