Admittedly I just picked the first speed versus fatality chart I could find with references (and they do link to the government site where the data came from).

Here's another study: https://www.aaafoundation.org/sites/default/files/2011Pedest...

This one shows a fatality rate of 2.3% for speeds from 10.0 – 19.9 mph, and 35% for speeds from 30.0 – 39.9mph. Even though the rate is different, it's still showing over a 10X difference in fatality rates at the higher speeds.

Consider this, at 30mph a cyclists body has to dissipate 4 times more energy than a 15mph cyclist. There's not much in a bike to absorb energy like in a car.