It could easily be changed but they are fine imo. IIRC the default respawn time of a vehicle is 60 seconds. Vehicles which have a longer respawn time have this declared in the respective *.vehicle file in the <vehicle> tag (first line). For example the patrol ship has this:
Code:
<vehicle name="Patrol ship" key="patrol_ship.vehicle" map_view_atlas_index="11" respawn_time="300" minimum_fill_requirement="0.5" existence="one_per_faction" reserves_spawn_point="1" >
respawn_time="300" means that the wreck will be cleared after 300s and spawning a new one in the process.