She says she was 15 years old but the age of consent in France is 15. In some other countries, it's even lower. In fact, Jerry Lee Lewis married his 13 year old cousin and it was legal.
So morally, what Bowie did can be viewed as wrong, but maybe he didn't do anything illegal. It depends on what the age of consent was in that state at the time.
Certainly, the episode shouldn't be buried and forgotten, it's part of his story, however much people dislike to hear it.
'When I saw the result, I threw up. My body rejected it.'