十五

In a sentence

• 我今年十五岁。

  I am fifteen years old.

  In this sentence, '十五' specifies an age, meaning 'fifteen'.

• 今天是农历正月十五。

  Today is the fifteenth day of the first lunar month.

  Here, '十五' refers to a day—specifically, the fifteenth day in a month.

• 这个衣服打完折后只要十五块钱。

  This piece of clothing costs only fifteen yuan after the discount.

  In this case, '十五' represents a specific numerical value, 'fifteen', used as an amount of money.