You may want to scan for files on a FTP server every 15 minutes. A Loop could be coded in a Project to first perform a FTP task (which scans for the files), followed by a Delay task to wait 15 minutes before trying again.
From within the Project Designer page, expand the Loops folder in the Component Library, and then drag the Delay task to the Project Outline.
On the Basic tab of the Delay task, specify values for the following attributes: