If he's sleeping up to 2.5hrs during the day then 10-10.5hr night is just about right
I would try actually an earlier nap & waking him up 2hrs into it & doing an earlier bedtime
5.30 - wake
12-2pm - nap
7pm - bedtime
Then you could try to push the nap out until its closer to 12.30pm & do 7.30pm bedtime, which will hopefully lead to a later wake up time. But I do think that at the moment the 6.5hr stretch before nap time is quiet long for his age
The av is 13hrs for toddlers, so if he's doing that at the moment, you won't be able to get him to sleep anymore unless you even the hours out between daytime sleep & night.
hth
Layla