Are gas station owners really going to set aside one or two pumps for E15, and label them? Consumers would then be faced with 5 types of gasoline choose from: base, mid-grade, premium, E85, and E15. Some people will be confused and put E15 in pre 2007 vehicles. Others will be confused and shun E15.
EPA should have waited to see if E15 was good for all "modern" vehicles, and then switched E10 to E15, since they are apparently required to enrich the corn farmers and ethanol refiners.
People running E15 should expect to see a small degradation in fuel economy. Since ethanol is about 25% less energy rich than gasoline, switching from E10 to E15 should look like a 1.3% fuel economy reduction, or about 0.4 mpg in a car that averages 27 mpg. Switching from E0 to E15 will cost about 3.8%, or about 1 mpg.