Billman, lots of variables. Attachments, load, speed, wheel weights, weight of the driver, and the list goes on. 15 to 20 degrees seems to be pretty close to the pucker factor. Remember, a hidden stump or hole will change your angle pretty fast. Just take it slow and easy and you 'shouldn't' get in trouble.
On my B6100Dt, filled rears, FEL and back blade, with the wheels pushed out 6 inches futher than the factory settings, I can place it on a 25 degree slope and hang off the downhill side without the wheels coming off the ground. <font color=red>(Kids, don't try this at home. The tractor wasn't moving, tied to prevent rollover, and I had a friend as a spotter. Just in case.)</font color=red> So, I decided that my pucker kicks in around 15, and at 20, if I got to move, it's real slow. And, that's with implements low, never high.
Keep the greasy side down.
Mike