I would do the shorter nap in the am and longer nap in the pm. Too long of a morning nap can cause EW, rob from night sleep, and lead to OT if it prevents the pm nap from happening. I would try something like this:
6 am: wake
10:30 - 11:15: nap
2:15 - 3:45/4: nap
7: bed
If you are going to shorten the am nap, I wouldn't do it all at once. Rather I would shave 15 minutes off the am nap and add it to the pm nap every few days. What do you think?