[sevlex]

If your engine is not designed for E15, you may regret using it.

[cableguymn]

says on the pump all engines 2001 and newer are approved for E15..

I can’t say anything I’ve put it in has complained.

[VideoDoctor]

If your engine is not designed for E15, you may regret using it.

You "may" want to change your wording from "may regret" to "will regret".