Which number should come next in this series? 25, 24, 22, 19, 15, _____?

Which number should come next in this series? 25, 24, 22, 19, 15, _____?

Explanation

Let's analyze the pattern:

25 - 1 = 24

24 - 2 = 22

22 - 3 = 19

19 - 4 = 15

15 - 5 = 10