Do you have a door closer that says, “Listed Door Closer Body 615R”, if you do you probably have an International Door Closer.  This is the UL number, which is a testing laboratory.   UL stands for Underwriters Laboratory, which started in 1894, to test electrically and fire equipment.  It does not tell us which door closer you have, but it narrows it down.   Another number we find on closers is 149A and 320 G, which are also UL numbers.  The best way to proceed is to find out as much as you can about the door closer you have.   I would look for Manufacturer (Corbin Russwin, LCN, Norton, Yale, International, Sargent, ect..), possibly a model number,  the hole spacing of the hydraulic cylinder (3/4″ x 9-1/16″, 3/4″ x 8-3/16″, ect…),   how the door closer is mounted (on the door, top jamb, push side, pull side).  I would then proceed to our Door Closer Information web page, and match up your hole spacing.  Or you could go directly to our International Door Closer webpage, and select the correct door closer.