I just read in another of your posts that you're about 5'6". While this Trek could be a good deal if it's in good shape, I think it's going to be too small for you. 15" was the smallest frame made for that bike and it was probably aimed at riders around 5'2".

Also, just an opinion... You may want to consider a road bike. Not necessarily a racing bike, but a bike with drop bars and slick tires. The less-upright posture reduces wind resistance, making long rides that much easier. Narrower slick tires like those found on a road bike will lessen rolling resistance, also making the ride easier. Of course, a hybrid could be fitted with road-appropriate tires, but you'll still be sitting more upright, your body acting as a drag chute.