Offroad tyres would help, but it is probably more technique than anything else. Riding deep gravel is much like riding sand. 10 mph speed limit may make it tricky, but you may find it easier if you stand on the pegs, keep your weight over the rear wheel and enough revs to keep the front wheel skimming over the surface. You steer with your feet by weighting the pegs. Control speed by slipping the clutch. If you chop the throttle or use your front brake, you will cause the front wheel to dig in and may end up dropping the bike. Might be worth your while getting some formal offroad training, especially if you intend to do more offroad than just this gravel road.