Good job on 15 miles, it's nice to start building distance.
A cool shower right after can help prevent some soreness later. I find that a warm shower makes me more sore. Advil can help with soreness too. Stretch later in the day and the next day. It's easy to lose flexibility from cycling. Drink lots of water. Seriously, lots (8-9 8oz glasses a day more of you're really sweating.)
What my trainer recommended whey protein as recovery snack. I usually schedule my rides and workouts so my morning or afternoon snack hits right after and will have a smoothie with berries, whey protein, soy milk and a small amount OJ. Or some mixed into skim milk. I don't usually need it after a short bike ride as I do after an intense training session. Feeling light headed, nauseated and a bit shaky is a sign that you need something to replenish blood sugar. If you're not feeling that, don't worry about it. If you're really feeling run down, eat a banana, the potassium will help. Don't eat or drink (non water drinks) too much though, good exercise isn't an excuse to indulge.