Electric scooters aren't really designed for hill climbing. It is much easier to simply pedal with your legs and push the scooter as you would an ordinary bike. The extra load of the battery may cause some of the problems. If the battery is heavy, it may affect the balance of the scooter. There is no reason why you shouldn't be able to ride a scooter up to a 15 degree incline.
The bigger problem comes if you have to climb up a steep incline and then take a big, fast decline back down. If that happens, you may not be able to control the scooter well. If the scooter starts to turn Off Road Electric Scooter over, you may be thrown off and hurt.
If you want to ride an electric scooter uphill, you should make sure that the throttle is set to slow. This way, you will be able to control the speed of the scooter so that you won't overspeed. Once you arrive at the top of the hill, you should set the throttle to normal and coast up until you reach the top.
At the top, you should turn around and begin to go downhill again. If the electric scooter has a big enough motor, it will be able to handle the steepest declines.