Hi!
I found an example in the excellent Logparser Helpfile (topic: Frequently Asked Questions) and modified it to your needs:
SELECT *
FROM <logfile>
WHERE TO_TIMESTAMP (date, time) >= SUB( TO_TIMESTAMP ('<your_time>','hh:mm:ss'), TIMESTAMP( '15', 'mm' ) )
If you want the last 15 minutes from the current moment you could use
SELECT *
FROM <logfile>
WHERE TO_TIMESTAMP (date, time) >= SUB( SYSTEM_TIMESTAMP(), TIMESTAMP( '15', 'mm' ) )
cheers
swobi