WW, I believe they were all standard Guild dread bodies - probably some small differences
in overall depth, neck thickness, nut widths. Aesthetically the
D15s seemed more "finished" and up close - visually somewhat upscale compared to the D4s.
IME none of the D15s, D4s or hogtop 25s could roar quite like a good spruce-top D25,
but they had their own tonal characteristics which could be appreciated. The last hog top D4 ('99) I sold
felt noticeably lighter than the last D15 I sold ('84), but I don't recall weighing on a scale to accurately compare.
The grain of the woods if you look closely varies quite a bit among Guild hog dreads - didn't compare side
and back wood, but from the front, here's an example of some: