Of the 15 items you can include, being a member of a club that met for about 2.5 hr/mo over 2 academic years is likely to be the least important and the one that you could most safely delete if something more important came along.
That said, if the club said something about your hobbys/interests that isn't otherwise reflected in the application, it might worth including it but if it was a club dedicated to learning more about an academic subject like chemistry, then it might not be of great interest to the adcom.