Airliner glide ratios fall between 15 and 20, which is comparable with cheapest immediately post-war training gliders for category B, aka the gliders you put a

Airliner glide ratios fall between 15 and 20, which is comparable with cheapest immediately post-war training gliders for category B, aka the gliders you put a student pilot to learn how to make turns before the advent of two-seater trainer gliders. And that 15 to 20 glide ratio is for best possible condition.