While I couldn't find any characters with more than three or four readings in this list, the Taiwan list (https://language.moe.gov.tw/files/people_files/%e5%88%

While I couldn't find any characters with more than three or four readings in this list, the Taiwan list (https://language.moe.gov.tw/files/people_files/%e5%88%9d%e7%a8%bf.pdf https://language.moe.gov.tw/files/people_files/%e5%88%9d%e7%...) has one character with five readings (著) and one with six (和). Still a long way from 15, though.