What is the age of consent for a US Citizen engaging in noncommercial+consensual sex with a foreign person in a foreign country?

Question involves criminal law concerning age of consent & US citizens in foreign nations.
Case Study:
Would it be legal for a 20yo U.S. citizen to engage in consensual sex with a 15yo Korean citizen, while in Korea?
-Age of consent in Korea: 13
-Younger person's parents approved of the relationship.
[1] PROTECT Act of 2003
(c) Engaging in Illicit Sexual Conduct in Foreign Places. Any US citizen admitted for permanent residence who travels in foreign commerce, & engages in any illicit sexual conduct with another person shall be fined/imprisoned.
(f) Def. The term "illicit sexual conduct" means a sexual act (as defined in sect 2246) with a person under 18 years of age that would be in violation of ch 109A if the sexual act occurred in the special maritime & territorial jurisdiction of the US.
[2] Ch 109A
Minor-Whoever, in the special maritime/territorial jurisdiction of the US
(A) attained the age of 12 years but not the age of 16
(B) & is at least 4 years younger
~What is the meaning of the "if" statement in (f)?
-a hypothetical "if" the sex act would have happened in the jurisdiction of the US instead
-or must it take place in the jurisdiction of the US