Oh, you'll get lots of different views on this one. I'll give you our experience. Our son is just now 15 mos and we've been on one nap now for about 3 weeks. It's not all super great and awesome from the get go, at least not for us, but we're not turning back now.
He started to show signs around 11 mos that two naps were not going to happen easy. So, after much reading up on it, I tweeked his schedule how I needed to in order to keep two naps as long as I could. I ended up spreading his sleep out a bit more by waking him up at the same time each morning, and not letting nap one go over an hour so the second nap could happen, then also not letting him sleep more than an hour for the second nap, give or take a few mins.
This worked well for 4 months. Then what started happening was the second nap had to be later and later or he just wasn't going to take it. Then his nights started getting shorter and shorter.
In the beginning we delt with some night wakings and a few early wakings, before 6am. Due to him being over tired. Their bodies need time to adjust to being awake for two long stretches day after day. It's still not perfect because we are in an early wake (6:30am), and an early bed time (6:30pm) cycle at the moment. But I expect that to correct itself soon. It was similar when he went from 3 naps to 2 around 7 months.
I'd wait it out as long as you can, especially if you have issues with sensitivity to overtiredness. The closer you can get them to 18 mos the easier the transition will be. For most, not all, of course.