I would have expected much more damage, from your heavy 15.89 pellet, traveling almost 700 FPS to be honest.
My truck's clear, plastic headlight assemblies were 15 or 20 years old, and became old and "cloudy".
After several unsucsessful polishing attempts, I replaced both of them with brand new headlight assemblies.
I removed the glass light bulbs, and proceeded to use the old assemblies, as airgun targets.
I was absolutely amazed by the holes generated by a .22 air rifle, in plastic.
The holes were perfectly round, with no cracks or breaks in the thick, brittle plastic.
It looked as if I drilled holes with a sharp drill bit.
Strange, and not at all what I had expected.
I agree with dv8oed....
I would use this opportunity, to experiment further, with slow motion video, and further testing!
Turn lemons, into lemonade!