A 15-inch (or 1000mm+ class) multirotor isn't just "big FPV"—it's light industrial equipment that happens to use FPV for visual reference. This is where hobbyist technology meets commercial aerospace principles.
13 Inch FPV Droneis a fundamentally different class of aircraft with distinct engineering challenges and use cases. This is the domain of extreme endurance, heavy lift, and professional/commercial applications.