The AP 115 is a controller based access point only. Essentially it has 2 operating modes that serve clients - Campus AP, and Remote AP. Campus APs build GRE tunnels to the controller and are typically used within your LAN. Remote APs build IPSec tunnels to the controller and do everything else within the confines of that. This is typically used outside your LAN when the connection is insecure (typically from the Internet).
If you wanted to get a controllerless ap you would need the instant version, in this case the IAP-115. The instant versions can operate in 3 modes that serve clients - Instant, Campus, and Remote. The additional one, instant, allows one access point to act as the virtual controller and keep a unified config for all access points in the cluster (one cluster per vlan). The access point can also be converted into the other 2 modes discussed above.
A campus access point (AP-x) can never be converted to instant, but an instant access point (IAP-x) can always be converted between all 3 modes.