I tried this quer caused problem:-
/* DELETE ln_bill
WHERE ROWID IN (SELECT ln_bill.ROWID
FROM ln_bill a,
ln_pmt_schedule b
WHERE a.acct_type = sAcctType
AND a.acct_no = sAcctNo
AND a.status IN
('Unsatisfied', 'Deferred', 'Skipped')
AND a.TYPE_ NOT IN ('Loan Fees', 'Late Fees')
AND a.acct_no = b.acct_no
AND a.acct_type = b.acct_type
AND a.pmt_sched_id_no = b.pmt_sched_id_no
AND b.status = 'Closed');*/

Then tried this one although added index at PTID other also caused a problem:-

DELETE LN_BILL
WHERE PTID IN (SELECT LN_BILL.PTID
FROM LN_BILL a,
LN_PMT_SCHEDULE b
WHERE a.acct_type = sAcctType
AND a.acct_no = sAcctNo
AND a.status IN
('Unsatisfied', 'Deferred', 'Skipped')
AND a.TYPE_ NOT IN ('Loan Fees', 'Late Fees')
AND a.acct_no = b.acct_no
AND a.acct_type = b.acct_type
AND a.pmt_sched_id_no = b.pmt_sched_id_no
AND b.status = 'Closed');

U said that the query caused a problem and u forget to mention it as i understand from the title the query is too slow so try to use the = in he where cond. rather than the in expression the scond advice is to create an ndx on every field in the where cond. ( if not exists) thanks