OMG it is 11:37 pm and I will be having nightmares after seeing that.
In legal terms, “they knew what they were doing” has no meaning when applied to underaged girls. The age of consent strictly defines that question, in fact it is the reason for an age of consent, to negate any implied permission — the only question is where to set the age of consent but that was already determined at the time of the alleged acts. I am not an expert on the law that would apply here, the acts presumably took place in different jurisdictions and I don’t know how the courts would interpret jurisdiction on board an airplane between one jurisdiction and another.
After a few days of that sort of legal wrangling, the trial would presumably get around to testing guilt or innocence within the framework hashed out on age of consent. But I doubt that 15 is going to escape definition in any U.S. context, maybe in the Middle East it would be acceptable.