My brother occasionally pulls 20 ton dumptrailers with it, and has just bought a 15 ton dumptrailer for his 6718. In a flat country like here, it works as long as you know what you're doing, and have your trailer brakes in order.
I've pulled 15 ton with the 5245 and YES, you need
hydraulic brakes, and be careful with potholes because the 10m3 manure tanker had 3 ton drawbar pressure..
Zetor axles are beefy and take more than the 3600kg on the serial plate, but i just dont want to take any risk..
If you plug the brakes in to your auxilary spool valve and operate it by hand, you dont have to use the tractor brakes at all.