Hi M.,
My daughter is almost 16 months and has been doing the same thing since she turned 15 months. Until a few weeks ago she was taking two 2 hour naps a day...no problems. Then, all of a sudden, the nap strike began. I am currently trying to move her to one nap a day. She gets really cranky in the morning but I try to push her to noon in the hopes that she will take a 2 hour nap. We have moved her bedtime down because by 5:30...she's a mess.
One thing that has worked for us during previous nap strikes is to just set the naptime schedule and put her in the crib for a predetermined amount of time. If you want him to take an 1 1/2 nap....then keep him in there that long -- regardless if he's crying, playing. Of course, if she does cry, I'll go in once just to make sure things are okay. This has worked for us in the past.
It is frustrating when they do this. But I do think it is very important for them to get good naps at this age. The more rested she is, the happier she is. And me too for that matter.
Good luck and if you find something that works...let me know!!