Hi Unfortunately even if you have closed the project the content remains in
the simulator. You have to restart the game to eliminate them which is
annoying. There is a topic related to this, even for texture change you have
to restart the sim. A voting has been created:
https://devsupport.flightsimulator.com/t/3099 For the FPS impact / render
distance I recommend to read the SDK LOD section:
https://docs.flightsimulator.com/html/index.htm#t=Asset_Creation%2F3D_Models%2FLoDs.htm
And the principals:
https://docs.flightsimulator.com/html/index.htm#t=Asset_Creation%2F3D_Models%2FGeneral_Principles.htm
To be honest this sim is suprisingly good optimized. It can really render huge
amount of vertices and materials at the same time. Of course when XBOX is out
we have to be more careful. But compare to FSX the limits are much higher,
still LOD is a must.