

Автобус придёт через пятнадцать минут.
The bus will come in fifteen minutes.
Это стоит пятнадцать рублей?
Does this cost fifteen rubles?
Нашему сыну пятнадцать лет.
Our son is fifteen years old.
"пятнадцать" is in the lesson "Numbers" (Level 3), along with 19 other useful words. LinDuo has 180 topic lessons like this one, 2,380 words in total. Every word has an illustration, a transcription and pronunciation in a female and a male voice. Just 10–15 minutes a day is enough to learn them all. Free, and works offline.