I found a 15-91 in a table for free on craigslist. I just love it! It sews so smoothly. I bought it to use on upholstery or heavy fabrics, to spare my regular machine. It really is a nice machine, and it sews beautifully. You're right about being able to sew over pins. I've done this my whole life! I really shouldn't do it, but it's so much quicker.
I'm making a Civil War Journals quilt, and will use my 15-91 just because it 'feels right' to use it on reproduction fabric.