What number comes next in the series 5 15 5 18 5 24 14 20 ?

Hard Number Series Puzzle

5

write the numbers in ascending order in words as onE twO threE fouR and so on
Replace the last letter in each word with position of letter in the alphabet (E=5, O=15, E=5, R=18 and so on)

so next number is ninE (=>5 as answer)