About intervals

Hi all.
I have a table with some timestamps fields. For example this table:

              date1        |         date2       
-----------------------------+---------------------------
 2004-03-01 11:20:00 | 2004-03-01 11:55:00

If I do a query like this, I get:

 SELECT date2 - date1 as diff FROM table;
 diff 
-------
 00:35
(1 row)


 but if I do a query like this, I get:
 SELECT date2 - date1 as diff FROM table WHERE date2 - date1 >= interval '15:00';
 diff
------
(0 rows)

What can I do to do a query like the previous one , and get the right answer??

Thanks !!
==                                 ==
   Pablo A. Velasquez Rivas
Computer Science Engineer
==                                 ==
All programmers are optimists -- Frederick P. Brooks, Jr.