In our Application, while a user faces a performance issue, we usually perform java tuning and Postgres tuning for Postgres users. But please also check if the file given in the below directory is present.
SupportCenter/pgsql/ext_conf ----> postgres_ext.conf
ServiceDeskPlus-MSP\pgsql\ext_conf ----> postgres_ext.conf
If the file is not present, then the Application defaults (hard coded in the Application) to the lowest parameters which would only make the performance of the Application worsen.
Please make sure those to add that detail to be checked while debugging a performance issue.