I had no idea a bike would could 1000+ when I first went in the LBS. A 15 mile ride might be bad for your knees. No matter what way you look at it your going to spend a bunch. Thing to consider most is comfort for 15 mile ride. Your hands and butt should be comfy. At an upright position your body would act like a sail and slow your riding a bit. I don't know much about tires but my CX ritchey tires take 75 lbs and at 195 I flatten them a bit, hence slow my riding. So if your heavier you might need tire that'll support your weight.

Go to the LBS and test ride every thing for a while. You'll be surprised how frames and components feel on the body. Even if your not going to buy one try them out. You might in the future.

Don't forget you'll need a pump, helmet, and pedals. Don't be turned off at old road bikes if you can get a functional one for your budget.