All credit goes to Nasdero and Kengglol for this.
I've been having some serious server fps issues used to run around 45 ish then dropped to 8-15 and i couldn't work out why.
I've rented a new Dedi box installed vanilla and then added mods - only 1 player on - same issue as above.
I came across this post:
I removed the Bell heli from 2 servers and bang fps back up to 45+
3 steps you need to do.
1 delete all pooh_13 objects in your objects_data table
2 to stop re-spawning delete all pooh_13 lines in the dynamic_vehicle.sqf make sure last entry comma removed (epoch_server)
3 remove the entry pooh_13 in the mission.sqm file (mpmissions)
not only has FPS increased but the server CPU utilization improved
hope it helps
Cheers