IRM S_AUDIT_ITEM Table update

Dear Support,

We have around 40million records in S_AUDIT_ITEM table and IRM process is updating this 40M records with the below query.

UPDATE S_AUDIT_ITEM SET S_AUDIT_ITEM.BC_BASE_TBL = (SELECT BC.TABLE_NAME FROM S_BUSCOMP BC WHERE S_AUDIT_ITEM.BUSCOMP_NAME = BC.NAME ) WHERE S_AUDIT_ITEM.BC_BASE_TBL IS NULL AND EXISTS (SELECT 'FOUND' FROM S_BUSCOMP BC2 WHERE BC2.NAME = S_AUDIT_ITEM.BUSCOMP_NAME)

This process is taking lot of time, we are in DB2 and we followed all the IRM settings for DB2. Is there any other settings to improve the performance of the query?