10 to 15% doesn't seem all that steep, at least around here. I've got one bank in the pasture at the other farm that's probably closer to 20% that I mow with my Super C tricycle a couple times a year. Granted I do have rear wheel weights, and double wheel weights on the front.
It's not that uncomfortable going across, but coming down the hill to make the turn, I do idle it down, and make the turn slow. But I'm running on good solid ground.
With mounted cultivators, it should lower you center of gravity a good bit. And if you're cultivating, you more then likely will just be creeping along, or at least not faster than first gear.
A lot of it's common sense, like making the turns etc. If you don't feel comfortable with it, maybe get something like a Super A, 130, or 140.
I am however, thinking depending on the type of soil you have. In tougher ground, it may have a tendency to drag you down the hill some, or sandy ground, just drift some. I'm thinking you'll be doing some oversteering to compensate the draft, no matter what you use.