SELECT rownum id, TO_DATE('01-MAY-2015') + ROWNUM/24/4 - 1 AS colA
    FROM (
        SELECT ROWNUM FROM (
            SELECT 1 FROM DUAL
            CONNECT BY LEVEL <= (TO_DATE('01-SEP-2015') - TO_DATE('01-MAY-2015'))*24*4
        )
    );

ID      colA                    colB
=====   ====================    =====
11089   23-AUG-2015 12:15:00    75667
11090   23-AUG-2015 12:15:00    64552
11091   23-AUG-2015 12:15:00    26633
11092   23-AUG-2015 12:15:00    86463
11093   23-AUG-2015 12:30:00    77364
11094   23-AUG-2015 12:30:00    2233
11095   23-AUG-2015 12:30:00    32213
11096   23-AUG-2015 12:45:00    73112
11097   23-AUG-2015 13:00:00    1238
11098   23-AUG-2015 13:00:00    8222