In 1911 JP Johansson was granted Swedish patent number 38643 for the 15 degree jaw angle on adjustable spanners. Decreasing the angle enabled the pinion to be moved closer towards the fixed jaw, which meant that the rack becomes shorter and doesn't protrude outside the head, which is advantageous in tight spaces. Another advantage, not mentioned in the patent, is that 15 degrees is the optimal angle for hexhead nuts when you flip the spanner. Bahco used this jaw angle on all adjustable spanners starting from the 2nd generation, except on the 80-series. In the photos you can see a 2nd generation No 52 and a first generation No 2.