繰り返し間隔は正確に同じですか?
関数EVALUATE_CALENDAR_STRINGで構文を確認できます。
DECLARE
next_run_date TIMESTAMP;
BEGIN
FOR i IN 1..10 LOOP
DBMS_SCHEDULER.EVALUATE_CALENDAR_STRING('FREQ=DAILY;BYHOUR=00;BYMINUTE=15;BYSECOND=0', NULL, next_run_date, next_run_date);
DBMS_OUTPUT.PUT_LINE ( next_run_date );
END LOOP;
END;
2016-10-08 00:15:00.239127
2016-10-09 00:15:00.239127
2016-10-10 00:15:00.239127
2016-10-11 00:15:00.239127
2016-10-12 00:15:00.239127
2016-10-13 00:15:00.239127
2016-10-14 00:15:00.239127
2016-10-15 00:15:00.239127
2016-10-16 00:15:00.239127
2016-10-17 00:15:00.239127