Hi Karthikeyan,
So plenty of discussion on Java 8 and non heap values for metaspace and compress class. Your initial question was what heap size has not been answered.
I presume the 3 instances are currently set to default CF10 setting of maximum 512m or -Xmx512m in JVM.CONFIG. Before suggesting a value how much free RAM does TASKMGR display?
Regards, Carl.