While it's true that the starting DL only has Lowell over 300, he's still Lowell. Further, the rest of the DTs are pretty big as well:

SR DT Lowell Lotulelei is 6'2" 320
SR DT Filipo Mokofisi is 6'3" 290
JR DT Alani Havili-Katoa is 6'3" 307
SO DT John Penisini is 6'2" 307
SO DT Leki Fotu is 6'5" 323
FR DT Hauati Pututau is 6'3" 288
FR DT Pita Tonga is 6'1" 287

I think we'll be just fine stopping the run. I do worry about the pass D. Fitts is an elite DE, and Anae looked good as a true freshman, but there's not a lot of experience at that position, and if we can't get to the QB quick and often I'm worried about our secondary.