From a T-SQL perspective WAITFOR DELAY will not actively use any server resources other than the overhead of having it keep an open thread using a little memory for the request and having it effectively do nothing.
From an SSIS perspective, if it issued the T-SQL batch out of a Script Task then the SSIS package will remain running. So again, it won't be actively using CPU or doing I/O, but it will be occupying memory on your server.
PS I am confused though. You say that you check a folder every 15 minutes but then you show a SQL batch. Are we talking about an SSIS Package checking a folder or a T-SQL process checking table?
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