I do use a HydraPak and do ride more than 15 miles. I do so b/c of the situation with my left arm that makes grabbing the hose easier/safer than reaching for a bottle (I have very limited use of my left arm/hand). Anyways, a traditional CamelBak does become uncomfortable but the HydraPak I'm currently using has spacers so it doesn't sit right on my back but rather 1/2 inch or so above it. It is cycling specific and it does help with the comfort issues. It was given to me by a LBS owner and I don't know the model.

All that said bottles would be better and the hope that I can improve my left hand grip enough to steady the bars while I reach for a bottle (and maintain my line) is the primary reason I'm doing yet one more surgery next month.