H.A.
We moved my twin boys to one nap around 15 months because the daycare they were moving to only did one nap - so they weren't exactly willing. However, it worked out well and their afternoon nap became much more consistent and even longer! (Mine were always bad nappers.) Anyway, we would put them down at their regular AM nap time, but wake them up after 10-15 minutes. It's hard to do (we're always told to NEVER wake a sleeping baby) but within about a week they wer down to one nap pretty consistently. They dropped the morning nap because it wasn't worth it and took an afternoon nap between 1-3! It worked like a charm in the end. HTH