Unfortunately, relative the current supply/demand imbalance it seems that exports would have to triple to restore equilibrium .... but that's just on one week of EIA data which may be skewed by refiners holding off on purchases in a wait for even lower prices .... in any case exports are only 5% of domestic production, so not a very big factor. Maybe that will change in the long term, but it seems unlikely short term.
The EPA claims it is OK to use E15 in newer cars but many others disagree. Most manufacturers say using it will either void the warranty or they will not cover damage caused by the use of E15 in cars not designed for it.