These random wall panels are the ones I'd suggest to replace with something. They look odd.
A simple concrete or metal surface would look better in my opinion, maybe some leakage from those drains on the edge. And some more orderly paneling on the side of the building.
I'm working on lod objects now, i have remade fuel tanks with a regular geometry and with less poly, with medium lod i have recover 3k poly with some other improvements, now i'm working in low poly object
For those suggestion i'm thinking for recover a bit more space from texture for add some others object and for do that i need to uvmap all again, when i have find a good solution i start improve it again