The weapon is the successor to the Franchi SPAS-12, and has similar pump-action/semi-automatic firing modes. In semi-automatic mode a gas piston drives a bolt carrier and rotating bolt. In pump-action mode the same components are driven by sliding the fore-end backwards. Pump-action mode is required to reliably fire low-pressure (less lethal) ammunition such as tear gas rounds or less-lethal bean bags. Switching between firing modes is done by pressing a button above the foregrip, and sliding the foregrip slightly forwards or backwards. The barrel is chrome lined and features screw-in choke tubes.
Unlike its predecessor, the SPAS-15 is fed by a detachable box magazine. The gun features a folding stock and a pistol grip safety.
In Predator 2, a Franchi SPAS-15 with an attached laser sight is used by LAPD Sergeant Reeger in the beginning of the film. Owing to his use of a laser sight, it is possible the weapon was loaded with slugs rather than buckshot.