The PD-3501G-AC is conforming to 802.1af, standard PoE that can deliver 15.4W at the powered device.
The AP-215 is fully compatible with standard PoE, however will disable the USB port if on standard PoE. From the AP-215 specifications (http://www.arubanetworks.com/products/networking/access-points/210-series/):
Power over Ethernet: 48 Vdc (nominal) 802.3af/802.3at compliant source
- USB port is disabled when using an 802.3af PoE power source; for unrestricted operation with PoE power, use an 802.3at compliant source
This is confirmed when I test the IAP-215-RW on the PD3501G with the command: show ap debug system-status:
....
Power Status
------------
Operational State POE-AF: USB port disabled;
----------------- --------------------------
Current HW State POE-AF: USB port disabled;
LLDP Negotiated POE Power 0.0W
....
So, you are good to go, unless you really need the USB port for a 3G/4G uplink or so...
No risk of overheating because of the chosen power injector, because you are working within specifications.