The numbers are different but the net result isn't. I took a 400 fps bb to the shoulder at holy wars at point blank range. I got a bruise out of it. I took a burst from a 330 fps AK at 4 feet at one of Alex's games and went away with a line of bloody welts. There are too many factors to consider when you are trying to draw the line of absolute safety which is why we draw a simple blanket rule at a level that reduces risk to an acceptable level.
There is no real difference between the types of injuries recieved from bbs at 330-400 fps. The bruise might be a little bigger, the welt might be a little deeper but that's all.
Once you get up to about 2.7-3 joules sort of area the Home office study found you started getting more penetrating types of injury which I think everyone in their right mind wants to avoid.
I therefore thing it's pretty clear that 1.5 joules falls well short of the threshold for unacceptable injury and every one should calm down.