The utilization could for a number of things:
- To many APs using the same channels or too close to each other
- Wireless devices taking to long transmit
- the power on your APs are too high
- Too many SSIDs
The show ap arm history and rf summary should give an idea of what's going on in your RF environment
You should also consider turning on drop broadcast / multicast if your company is not using any applications that requires multicast