The Olympus Body Cap Lens 15mm F8.0 does perform well optically with surprising sharpness in the center. Obviously, corners and edges are different story, which can be rather smeary in certain situations. It is likely caused by the limited optical correction capability as the lens has only three non-aspherical elements.
However, sharpness can still be better than expected if photographers take a little more time to make sure that the focus distance is correct and the object is placed in the central third. The Olympus Body Cap Lens 15mm F8.0 has a simple design and there are less surface and air-glass transitions for light to lose their intensity. This may result in very high contrast and brilliant color representations.