No, it's not too steep...
If you are truly concerned, after you chock the wheels and level the unit up, screw an anchor (like used for dog runs or awning tie downs) into the ground and attach your break away cable to it. That way if, for some reason, the camper decides to depart the pattern, the cable will be pulled, the brakes will activate, and it will stop.
I've done that in my brother's driveway which is very steep, but it proved unnecessary, though it made me feel better.
I'd say that the only driveway that is too steep is when you can't raise one end high enough to level because the other end is grounded.