Couchbase single node cluster high memory

I have a single-node couchbase cluster with 3 buckets A, B, and C, in the below state. The issue I am facing is that 88 percent of system memory is getting used not sure where is this memory consumed.
Also, I can see the ram used by the buckets shown on the couchbase UI is less than the one shown by couchbase metrics. Added the values below. Is this the side effect of the ejection method when it is not set? Pls help

Buckets---- RAM used/quota on couchbase UI---- Couchbase metrics(Prometheus)
Bucket A ---- 140MB / 3.9GB ----------------------------------- 2.8gb
Bucket B ---- 239MB / 3.09GB --------------------------------- 2.35gb
Bucket C ---- 41.7MB / 2GB ------------------------------------ 1.108gb

  • couchbase version - Community Edition 5.0.1 build 5003
  • data service 10175MB, Index Service 512 MB, Search Service 512MB
  • Node machine memory 15 GB
  • cluster quota 9.93 GB
  • All buckets are ephemeral
  • Ejection Method: No ejection for all 3 buckets.

@jayant304 , Couchbase 5.0.1 is fairly old and EOL already(Enterprise Software Support Policy | Couchbase). It would be a better idea to try out the latest community edition and see if that works out better.