"which means near constant braking"


This is the main problem. I have never had much trouble as long as I don't just ride the brakes (same can be said for brakes on a car on steep downhills). This isn't easy at 15% grades but even then, intermittent braking usually solves the problem. This often means slowing down more than you think you should when you do hit the brakes, using the front brake more, being more comfortable at higher speeds, etc..

This is a great problem to have though. You are lucky.