第十五天的英文是：Fifteenth day.
例句：
His birthday falls on the fifteenth day of the first lunar month.
他的生日是农历一月的第十五天。
Exactly, it is on the fifteenth day of August of the lunar calendar.
精确地说，它在农历的八月十五。
The Lantern Festival falls on the fifteenth day of the first lunar month.
每年农历正月十五是中国的元宵节。
The fifteenth day of the show smiling face, happy long continous happiness;
正月十五展笑脸，快乐长久幸福绵；
In the Han Emperor, has been ordered fifteenth day as the Lantern Festival.
在汉文帝时，已下令将正月十五定为元宵节。
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