[Crex]

Most of the Singer 15-30's I've seen are treadle or early conversion to motor type. Didn't look like they would handle the heavier threads like 207 and up. I'm no expert here with Singers, just my wife is a seamstress and she has more machines than I have anvils.......which is wrong the way I see it (does give me some leverage if I see a good one needing a new home).

From what I have been able to find so far on line, I'm not sure your machine will be able to handle heavier leather stock like multi-layered 7-8 oz or thicker. I'd test a stack and see before investing in a lot of needles/thread/bobbins etc. You can test without thread. If it will work with the leather stack you need to specify leather needles for that machine - they are stronger/thicker and have a special point design just for leather.

Since it is a Singer Clone, you should be able to get replacement needles, thread, etc on line with a little creative googling. I'll keep poking around on more info and see what my wife's contacts might have to say.
She's a long time active member of The American Sewing Guild. Not much different than The Knifemakers' Guild when it comes to networking.

Will get back with you if I find anything. Mean time, if you have some needles with the machine try some dry stitching with stacked/glued leather scraps same thickness as you would normally do a sheath.