Como descartar várias partições de intervalo com base na data?

DECLARE
    CANNOT_DROP_LAST_PARTITION EXCEPTION;
    PRAGMA EXCEPTION_INIT(CANNOT_DROP_LAST_PARTITION, -14758);

   ts TIMESTAMP;
BEGIN
   FOR aPart IN (SELECT PARTITION_NAME, HIGH_VALUE FROM USER_TAB_PARTITIONS WHERE TABLE_NAME = 'MY_TABLE') LOOP
      EXECUTE IMMEDIATE 'BEGIN :ret := '||aPart.HIGH_VALUE||'; END;' USING OUT ts;
      IF ts < SYSTIMESTAMP - INTERVAL '15' DAY THEN
      BEGIN
         EXECUTE IMMEDIATE 'ALTER TABLE MY_TABLE DROP PARTITION '||aPart.PARTITION_NAME|| ' UPDATE GLOBAL INDEXES';
      EXCEPTION
            WHEN CANNOT_DROP_LAST_PARTITION THEN
                EXECUTE IMMEDIATE 'ALTER TABLE MY_TABLE SET INTERVAL ()';
                EXECUTE IMMEDIATE 'ALTER TABLE MY_TABLE DROP PARTITION '||aPart.PARTITION_NAME;
                EXECUTE IMMEDIATE 'ALTER TABLE MY_TABLE SET INTERVAL( INTERVAL ''1'' DAY )';            
      END;
      END IF;
   END LOOP;
END;