The E15 is fine to run in a newer car. I've been running it in my 2017 Challenger 5.7 without issue. Minimal fuel economy loss...more noticeable in the winter than the summer. I actually started burning it back in 2017-2018 in my '02 Durango 4.7 right before I bought the Challenger, and had no issues with it in the old Durango.

Now my '79 LeSabre hates it. It's a 301-2bbl Pontiac motor...untouched original car. It burns through E15 like mad. I only tried it in the car twice, but you could damn near watch the fuel gauge drop while you were driving. When I put regular pump 87 in, this car gets 22-23 mpg on the highway without blinking.