A person who enjoys discussing their interests at length is likely to do what?

The most fitting choice in this context is "descant." This term refers to speaking at length about a topic, often in a detailed or elaborate manner. When someone descants, they delve deeply into their interests, sharing extensive knowledge and enthusiasm about the subject.

The other options do not align with the idea of engaging in lengthy discussions about personal interests. "Dilatory" refers to being delayed or procrastinating, which does not connect to discussing interests. "Contemn" means to regard something with disdain or scorn, which does not imply any enjoyment in conversation. "Descry" means to catch sight of something or detect it, which is unrelated to discussing one’s interests. Thus, "descant" is the term that best describes someone who enjoys lengthy discussions about their passions.