[Konstantinos]

No, it's not!

pawn Код:

public OnPlayerExitVehicle(playerid, vehicleid)
{
    SetTimerEx("OnPlayerVehicleRespawn", 3000, false, "i", vehicleid);
    return 1;
}

forward OnPlayerVehicleRespawn(vehicleid);
public OnPlayerVehicleRespawn(vehicleid)
{
    SetVehicleToRespawn(vehicleid);
}

You used a for loop to respawn all the vehicles everytime a player exits the vehicle. It'd be better to respawn the one they exited after 3 seconds. The rest will be respawned by the respawn delay.