Each vehicle inside network bubble reduces about one frame on client. It doesn't matter if I'm looking at them or how far away are they, so it's not render issue. It does not affect CPU, GPU or memory usage. It doesn't matter if they are spawned by economy or debug. This is very confusing because all physics calculations are server-side, and essentially everything except effects and lighting are also handled server-side. I tried disabling all client-side functions in the car script, but nothing changed. As you can see server doesn't even notice them, yet it is the one who should be doing hard work.

I'm running server on the same pc as client and there is no server FPS drop when client FPS drops, this proofs that it some kind of engine/scripts issue.
I'm working on a server which currently has 1500 vehicles spawned, server is working well with this amount, but it's unplayable, because there are always at least 30 vehicles in client network bubble at any point of the map, so clients suffer huge FPS drop.