I know about altitude cull and view optimization, but I don't know what settings. Is there a way to force KLAX to load earlier so this doesn't happen?
This doesn't have anything to do with altitude cull or the view optimization. It's the general loading range of the scenery which is involved, and it's nothing you can fix.
Right now, KLAX loads from 16 nm out from the airport center. If we reduced it in order not to load when parked at KLGB, which is about 14.5 nm from KLAX, it would fix this issue if you are AT KLGB, or if you are approaching from the south, or south-east. But if you are approaching from north-west, is just too close to KLAX.
Increasing the loading range, instead, would be wrong, because we would then allocate memory for KLAX objects when they are not needed, and risking OOMs, just to save you from that 2-3 seconds pause, is not worth it.