I just wanted to Chime in on this. I can say this is Component Size/Quads Related. If i choose a 255x255 quad and a with 2x2 sections and 1x1 components, the grass loads INSTANTLY every time.
Working your way up from there its when you get too many components into play it gets longer and longer as its calculating each section. Now from what i understand as you increase the resolution of the landscape that way, you also increase its verts and whatnot therefore making more calculations occur.
I could be totally off base with some of that 2nd part, but its what i noticed.