postgresql – find out why table insert is slow in postgres cluster

Recently i did create a PostgresQL-HA 11, cluster using bitnami helm charts.
There is 1 master and 1 replica, pg_pool and metrics.

I am using NFS as file storage for the cluster and it is connected to a vmware guest machine with enough memory and cpu and a HP fast hard disk drive, in same broadcast domain on same VSwitch with a 1Gbps v-port.

But insert into database using a js written batch script is slow like this:
Insert 2000 records in 13.952 seconds.

The script inserts very fast on my local non-clustered postgresql database, on my local machine and inserts 2000 records in less than a second.

So since I am not a DBA or someone like that, how i can find why it is slow? can metrics or sth else help?