At that age, dd1 was doing 45mins in the morning & about 1.5-2hrs in the afternoon & her routine was something like this:
6am - wakes
9-9:45 - morning nap
1-2.30 - afternoon nap
6.30 - bedtime
I think if your ds is sleeping 1.5-2hr in the morning, then he probably won't need an afternoon nap until at least 3.5hrs later. Some babies wouldn't even take an afternoon nap on a morning nap that long (or even as long as 1hr to be hoest) so its up to you if you want to shorten the morning nap or not... some babies do better on long morning nap & short afternoon catnap. I wouldn't expect the pm nap to be anymore than 45mins though & if it was, I would wake him up so that he can go to bed at the right bedtime. The latest I would let him sleep for a 7-7.30pm bedtime is 4pm.
Shortening the morning nap did wonders for dd1... she took a solid 1.5-2hr nap in the pm. Dd2 was a little difficult & there were plenty of times we were stuck taking 2 short naps. If you go down the route of shortening the morning nap, I would too look at doing it slowly... maybe cut 15mins or so every couple of days until you get to 45mins or 1 hr. Bump up the pm nap. On a 45min morning nap, my girls were able to stay awake for 3.5hrs max before they needed an afternoon nap.
hth a little
Layla
