The Parker 15 was introduced in 1983 and continued in production until around 2000. It is an inexpensive pen aimed at the school or student market. The red barrel has no imprint. The brushed steel slip cap has a chrome plated clip.  The cap is stamped around the lip "PARKER   MADE IN U.K.  IIA".  It was originally marketed as a cartridge pen, which are still available from most good stationers. This example is fitted with a cartridge converter (or "Refillable Ink Cartridge" as Parker calls them). This means that you can fill the pen as a conventional pen using ink from a bottle.  The converter can be pulled out easily and cartridges used if preferred.

It is fitted with a medium steel nib, stamped simply "PARKER".