I need to confirm this because we currently have 48 H320's connected to an ICX 7150-48P with the POW allocation for each port set to 7.5W which is fine if it's max is 6W, however, this is not a good idea if the max is 15W as the switch will best handle only 24 H320's considering it's POE budget.
The design document shows the maximum that can be requested by the device. It's up to you whether you build out your environment to the theoretical maximum or the real-world numbers you've seen. Personally I wouldn't be comfortable with pushing a POE switch to its limit so I would design as if the AP actually used 15W.
If for no other reason, having 48 APs on a switch causes a pretty nasty outage if that switch dies. Better to split them across two switches - IMO.