The best way to contemplate damage from E15 is to look at boats and old motorcycles that were damaged by E10. Specifically, hoses, gaskets, and other types of seals can deteriorate from exposure to ethanol.
Interestingly, there is an E85 conversion kit for my car: https://www.change2e85.com/e85-conversion-for-honda-acura-civic-accord-hybrid-integra-crv-4vah