If you are doing 10 mile rides and wanting to do 15 milers soon, or even 20 milers, then you really don't need a $100 short designed for doing centuries. Maybe later you'll need those! You can save some money by buying mid-range shorts for now. Look at TE's SALE shorts. You are not going to need heavy duty chamois for 20 mile rides, but *some* chamois would be nice.

Also as you get into longer rides, don't overlook the possibility of your SADDLE being the culprit of causing discomfort. If decent chamois don't solve it, it could be you'll need a different saddle. Some saddles are comfy enough for the first hour or so but become uncomfortable on longer rides. You won't know whether yours is like that until you start doing longer rides of 2 hours or more.