Looking at datasheet:
http://www.arubanetworks.com/assets/ds/DS_RAP-155.pdf
REGULATORY MODEL NUMBERS • RAP-155: APINR155 • RAP-155P: APINR15P
This is a RAP-155P.
All RAPs, AFAIK ship with IAP software and then provisioned to be RAP via activate or manually into IAP GUI.
How to find if the AP you have in your hand is operating in RAP mode or IAP mode?
1. If you have registered on activate, it can tell you that.
2. Can you open the local UI of the IAP, by putting its IP address in browser?
3. Does the AP broadcast SSID "instant" when its plugged in.
4. If you have the console cable to connect to 155, show version can help.
Notes:
If 155 is operating in RAP Mode, you can factory reset it, to have Instant software. Then connect to IAP via wired DHCP IP address or via wireless using "instant" SSID.
Standalone mode is a special mode of operation of an IAP, where the IAP does not from cluster with other IAPs on the same VLAN. That you can set, once IAP GUI is up by going to maintenance>convert>select IAP>standalone mode.