Link: Yeah, that was me that pointed it out. It varies by state. In Florida it’s 16 or 18, depending on circumstance, so as per Vic’s comment, since the younger girl is 15, it is technically illegal no matter what. As per Keith’s link, the specifics are:

The age of consent in Florida is 18, but close-in-age exemptions exist. The law is complicated, but it appears that it is illegal to have sex with anyone under 12; legal for a person under 18 to have consensual sex with someone 12 or older (Section 794.11), and it is legal for a person 18-23 to have consensual sex with someone 16 or older (794.05). Persons 24 or older, or who are over 18 and have a position of authority over the other person are only permitted to have sex with them if they are at least 18.

794.05 Unlawful sexual activity with certain minors.– (1) A person 24 years of age or older who engages in sexual activity with a person 16 or 17 years of age commits a felony of the second degree, punishable as provided in s. 775.082, s. 775.083, or s. 775.084. As used in this section, “sexual activity” means oral, anal, or vaginal penetration by, or union with, the sexual organ of another; however, sexual activity does not include an act done for a bona fide medical purpose Florida code, Title XLVI, Chapter 794

But moreover, those laws only apply to heterosexual relationships (in Florida) many states have differing laws for hetero and homosexual relationships and IIRC, in Florida, homosexual relationships are always unlawful and therefore have no age of consent.