Did you get the bobbin threaded correctly? I should have pointed you to
https://www.singer.com/support where you can find the manual at
https://www.singer.com/sites/default...%20Machine.pdf
If you look on page 13 of the manual or the bottom of page 6 of the pdf, it will show how the bobbin is supposed to be threaded.
I am of the persuasion that one should not alter the machine to accept 15x1 needles, but I do understand why some might. From my understanding there are only two sizes (12 & 14, I think) available new.
Actually, I live in Denver so I could go to "Ralph's" which services, sells and has parts for industrial sewing machines, so I could just go there and buy a bobbin to fit.
Janey - Neat people never make the exciting discoveries I do.