What is tier 15 adventure time?

I'm sorry, but as of my last update in October 2021, there is no official information or confirmation about a Tier 15 Adventure Time. The show, Adventure Time, ended after ten seasons in 2018. However, Adventure Time has a vast universe with numerous seasons, episodes, characters, and storylines that fans can explore and enjoy. If there are any latest updates or announcements about a potential Tier 15, it would be best to check with official sources or follow the show's creators and official platforms for any new information.