Use a where clause like this:WHERE
YourDateColumn >= DATEADD(mm,DATEDIFF(mm,0,GETDATE())-1,14)
AND YourDateColumn < DATEADD(mm,DATEDIFF(mm,0,GETDATE()),14)
This is really asking to start on the 15th of last month and go up to anything that is LESS than the 15th of the current month - which is the best way to do what you described.