Please Help Me To Optimize This Sql Query, It Takes 28 Seconds To Return Result. Please Give Me A Tips Where I Went Wrong?

SELECT * FROM
( SELECT TOP 15 * FROM
(SELECT TOP 15 CMDS.STOCKCODE AS CODE,CMDS.STOCKNAME AS NAME,CMDS.Sector AS SEC, CMD7.REFERENCE AS REF,T1.HIGHP AS HIGH,
T1.LOW,T1.B1_CUM AS 'B/QTY', T1.B1_PRICE AS BUY,T1.S1_PRICE AS SELL,
T1.S1_CUM AS 'S/QTY', T1.D_PRICE AS LAST,T1.L_CUM AS LVOL,T1.Chg AS CHG,T1.Chgp AS CHGP, T1.D_CUM AS VOLUME,substring(T1.ST,7,6) AS TIME,
CMDS.SERIAL as SERIAL FROM CMD7,CMDS,CMD4 AS T1 WHERE T1.ST IN
(SELECT max(T2.ST) FROM CMD4 AS T2 ,CMDS WHERE
T1.SERIAL=T2.SERIAL
AND CMDS.SERIAL=T2.SERIAL
AND T2.sd='20060821'
AND CMDS.sd='20060821'
AND T2.L_CUM < '1900'
AND CMDS.sector >='1'
AND CMDS.sector <='47')
AND CMDS.SERIAL=T1.SERIAL AND
CMDS.SERIAL=CMD7.SERIAL AND
CMDS.sd='20060821' AND
CMD7.sd='20060821' AND
T1.sd='20060821' AND
T1.L_CUM < '1900' AND
CMDS.sector >='1' AND
CMDS.sector <='47' ORDER BY T1.D_CUM desc)
AS TBL1 ORDER BY VOLUME asc) AS TBL1 ORDER BY VOLUME desc;