I’m gonna guess that the only way you will get these passengers on another cruise, especially a Carnival cruise, is to give them a free trip. A 15% discount implies that these people would spend their money again with Carnival. I doubt it.
Carnival has long been a poorly rated cruise line. I hope the southern ports will get the message & stop hosting these pig boat cruises.
If you base your buying decisions based solely on price you takes yer chances.