Hi Thamil,
nice to see someone else stay on Introscope 9.5.2, sometime I got the same problem.
In my opinion, a larger value for "introscope.enterprise.agent.metrics.limit" in the "apm-events-thresholds-config.xml" doesn't fix your problem. Try to increase "introscope.enterprise.harvest.duration" and "introscope.enterprise.smartstore.duration" from "3500" to "7000" to consider the slow smartstore access (the new values became active after some minutes without a Collector restart).
To reduce the collected metrics data in a easy way you can modify the "IntroscopeEnterpriseManager.properties"
"introscope.enterprisemanager.smartstore.tier3.frequency=900"
"introscope.enterprisemanager.smartstore.tier3.age=335"
to a smaller age value. You lost some old metrics data, but this removes lots of old metrics in a easy way (to activate the new values a Collector restart is necessary).
Try to find out the agents are reporting lots of new data, sometime we have some application problems and therefore some agents report lots of data.
Regards, Lutz