Postulation from anecdata (that is, I'm not being very scientific about this, just putting together stuff I've heard): could the 1500 grams rule have come from people wanting to breed their females early? I see a lot of threads about "power feeding" and trying to get females up to "breeding size" within one or two years instead of waiting the full three. From what I've gathered reading stories from breeders that have been in the hobby for a while, putting the females in too young tends to ruin the clutch anyway. They tend to slug out, and you just wasted your time and energy on a long shot project. I don't think I've seen anything relating to the long term health of the animal, but I wouldn't be surprised if it affected that as well