The details disappearing with the distance are just LOD levels, to keep the fps *up*, and are also related to your zoom level. If use a very wide setting, they'll disappear earlier, we usually optimize for a zoom level of about 0.70, which is widely considered the most realistic one.
KLAX might be a bit heavy with not so powerful systems, but it's very fast on fast systems, one setting that might affect performance is the HD Textures, you can try turning it off and see if makes a difference.
Of course, if you are running with lots of AI, considering the size and the number of parking spots at KLAX, the real slowdown it's caused by AI, not the scenery.