Exactly!
The main noun phrase in the sentence is "Whichever couple can hold the pose of the statue the longest," and the main verb is "wins."
In this sentence, the noun phrase serves as the subject of the verb "wins."
The entire phrase describes the condition or criteria for determining the winner of the competition.
So, in simpler terms, the sentence is saying that the couple that can hold the pose of the statue the longest will be the winner.