There's nothing that needs to be optimized, the scenery is as optimized as possible. There are only a couple of reports of frame rate drops on certain viewing angles and, all of them turned out to be other sceneries in conflict.
Use the free FSX Airport Scanner program to look for AFCAD duplicates and remove them all.
Note that not all duplicates could be found by that program so, even if it doesn't find any, it's not 100% sure there aren't any.