There is no way to specify different levels of data retention for element types, so to keep this data you will be keeping it for all core Orion data (modules, syslog & SNMP Traps have their own data retention settings).
In version below 9.5 open System Manager > File > Orion Network Performance Settings. Use the sliders to adjust the detailed and hourly data retention figures as you require. In 9.5, this is handled in the browser interface Admin > Polling Settings.
Obviously you need to have enough database storage to handle the settings you set, so keep an eye on growth.