My son went from 2 naps to 1 at 15mo. too. He was going to bed too late, and I finally figured out that his 2nd nap was taking away from his nighttime sleep. It was a smooth transition for us. I started napping him about 5 hours after waking (1pm for us), immediately after lunch. In the am we eat breakfast, play, we usually leave the house, then come home for lunch at 12pm. After lunch, everyday, we immediately go from the highchair to his bedroom for a nap. We do our regular routine, and he sleeps for 2 - 3.5 hours! We made his bedtime a little earlier as a result, but nothing drastic. I think he'll adapt find as long as he's ready & you keep a steady routine. Good luck!