Search from Organization Management Portlet is slow with large IDM database in EPP 5.2

Issue

Environment:

We have thousands of users and many custom groups in the Picketlink IDM database.

Problem:

Unresponsiveness occurs when we log in as root and use the User Management tab of the Organization Management portlet (/portal/g/:organization:management:executive-board/organization/management) to search for a particular user by (partial or complete) first name, last name or e-mail address. Searching by user name works fine, though.