I've just tried counting out loud from 10 to 20 and I stress the "teen". I agree that if you wanted to insist, as in your "fourteen/fifteen" example, then the first syllable would often be stressed.
Okay, maybe Australians count differently. We definitely stress the first syllable on a wider range of occasions than you.
How would a British newsreader say:
"Fifteen thousand people died in the earthquake".
In AusE, the emphasis is on "Fif".