My Singer 301 does a great job as long as I don't fill the bobbin too full. I use a Singer size 11 needle, feeddogs either up or down, a hopping foot, gloves and a piece of plastic. If I fill the bobbin past 2/3 full, then the thread jumps out. It doesn't with piecing but does with FMQ. She didn't like a Schmretz needle to FMQ the first time I tried, so I just keep Singers for her. It is another machine with a vertical bobbin. Sometimes I have to adjust the tension slightly for a really fine rayon embroidery thread, but rarely. I haven't tried with the 15 yet.
Muv, your FMQ looks good. You have my admiration using a treadle.