I personally try to compact them with PNGOut (and I can’t recommend other ways, since some of them may heavily reduce quality) and if it’s still above limit, convert to jpeg with maximum possible quality
So, for >>1385927 it’s probably just original file being unoptimized. I don’t see any compression dithering.
Tried it, 73.5 -> 68.9 and 39.8 -> 37.2, still far too much for an upload.
Doesn’t matter that much since the JPGs are already here, just thought it would be neat to preserve the originals if possible.