Kaaj,
What you really want to do is a true inear or multi-phasic linear load cycle.
Basically, you start at about 55% of weight, and then increase 5% every other work out until you hit 85-90% 1RM. At this point, you decide whether to go negatives and continue onward to up to 160% of 1RM (though I recommend no higher than 110-120%), or try some form of "cluster progression" and arrive at 95-100% 1RM (that is the 1RM at the beginning of your cycle; we're going to assume you got a little stronger.)
So, at the least, you get about 9 increments. That's 3 weeks of 3x-a-week training, still too short for what you want.
Then, to extend your cycle, you apply multi-phasic approach by acknowledging that higher load requires less frequent changeups. In your case, you can reasonably expect loads at 85% or higher to be used at least twice and be very productive. Tha's another week. Voila, your 4 weeks. If you want to do add more weeks, you just add a "change-every-3-days" phase (works well if you do negatives) and work out where the endpoints would be.
Problem is, now, how do you figure out your reps? You don't. You look through your journal and find out your 15RM cut-off point. Once you past the 15RM count, you go into cluster HST and work toward a generic rep count. You implement the descending-density variation of cluster training, and then after you set, throw in a burn set.
Now, philosophically, I prefer long, long cycles where load progresses at an "adequate" threshhold. And I like the structure of 15-10-5-N. What you want is the opposite of this; you want to go hard for a short period of time. In that case, it's best to loosen the structure and think purely in load, strain, and metabolic work. As you can see, the 10-15% increment stuff doesn't even figure into the equation.
cheers,
Jules