After the IAR's efforts finally paid off once they received the order for the IAR-14, Elie Carafoli was ready once again to start working on new fighter design. The result was the IAR-15 fighter, undoutably the finest of all his creations and the one aircraft of its pre-IAR 80 creations that could take on anything the world could throw at him.

Like all previous designs, the new airframe was also built from a combination of wood and metal and covered with duralumin sheets and pine plywood. This time the fuselage was also to suffer major changes together with the tail, wings, undercarriage and the engine. The cross section of the forward fuselage became round with a long-chord engine cowling, whilst the rear fuselage was enlarged in diameter and reinforced. A NACA type ring was mounted in the nose, covering the engine. The tail's shape and profile were modified from a round one to a triangular one. For the first time, the undercarriage was changed, becoming aerodynamically cleaner, since it consisted of a single strut with wheel spats mounted near the wing roots and, also for the first time, the tail "ski" was replaced by a small wheel.

Wings were shortened to just 11 meters and the wingtips were rounded furthermore to improve airspeed and maneuverability. It was suggested to fit the plane again with the infamous "anti-crash" pylon, but because of its notorious bad influence a rounded knob was mounted behind the pilot's head rest instead.

Several of the powerplants previously used were suggested, but the end Carafoli chose to abandon the classical in-line engines since they were either too heavy or simply not powerful enough for a fighter. Instead, a Gnome-Rhone 9Krse, nine-cylinder, radial engine rated at 600 HP at 4000 meters , was fitted to the prototype with very good results. As armament, the aircraft retained the standard pair of two synchronized Vickers 7.7 mm machine guns firing through the propeller common for all early IAR fighter projects. Each machine gun had a good 500 rounds supply of ammunition.