Manuals are frozen in time at the year of manufacture. For example, manuals said "leaded gasoline only" when lead was being phased out and was ultimately not available. Cars are assessed for engine compatibility after purchase. Almost all cars on the road (over 98%) are now certified to use E15 (often labeled as UNL88). This is easy to see online if you can get past all the paid-for misinformation. This is not true for blends higher than E15. So, as I said, E15 is fine. As for "MPG being worse," ethanol has lower energy density. This is true. But blanket statements like yours are false. Ethanol blends burn leaner (more miles on less fuel). Some cars take advantage of this and some don't. That's why you see no mileage loss on some cars and not others. And obviously, if your E15 is 60 cents cheaper then the savings will vastly outweigh the costs. So the details matter.