The processing has several steps:
trap arrives
event generated
event processed by EPP and some actions are executed.
It's important to understand on what stage the delay are. Can you check timestamps in snmp trap log, event log and alarm log to see where it's delaying?
Also, there's a built-in template for netxms server performance monitoring. If you upgraded from previous versions, that template does not get upgraded automatically (you need to change ImportConfigurationOnStartup server configuration parameter and restart the server, or you can take /share/netxms/templates/netxms_server.xml file from the file system of the server and import it using web/desktop client.