A 20-degree angle provides a more robust edge, while a steeper 15-degree angle offers more precision. Before altering your knives, consider that Western knives, generally made with softer steel, may not hold a narrower 15-degree angle for long and will require more frequent sharpening if this angle is adopted. (Japanese knives, made from harder steel, retain a narrower edge longer.) Also, changing the angle from 20 degrees to 15 degrees will result in the gradual removal of more metal over time.