Which is better B-15 or G-15 lenses?

B-15 and G-15 both refer to specific colored sunglasses lenses. The B-15 are brown in color, which offers slightly heightened contrast as they block a bit more of the blue color spectrum. G-15 are a gray/green colored lens originally developed by Bausch and Lomb in 1951 for the Navy Air Corps as the N-15. It was through minor reformulation for prescription use that the designation was changed to G-15. The benefit of the G-15 lens is that it transmits natural color to the eye, so that while everything appears darker (as 85% of the incoming light is blocked, the same as with the B-15), the color of what you are looking at is not influenced by the lenses. What you are using your sunglasses for, and your own preference are the way to determine which you prefer. From a perspective of natural eyesight, the G-15 is technically superior.