Automakers continue to quietly void warranties if you use E 15 gas.

States are dropping the minimum 87 octane requirement under blackmail from the oil refineries who threaten to cut off supplies of fuel during high demand times unless they are allowed to ship 83 or 84 octane gas and bring it up to 85 or 86 octane with ethanol. However, almost all cars made in the last 30 years are designed for 87 octane minimum, and will have potential engine damage and voided warranties if the lower grade fuel is used.

Also note that "premium" has gone from 93 octane to 91 octane in most places.