In Japan, the legal age for marriage is 18 for both men and women. 15-year-olds are not allowed to get married without special permission from a court or other authority figure such as a parent or guardian. There are some exceptions where 15-year-olds can legally marry in Japan without parental consent or special permission, but these exceptions are rare and difficult to obtain. Additionally, there is considerable social pressure against underage marriages and potential legal issues that could arise if one partner is much older than the other. It's best to wait until at least 18 years old before getting married if possible.