the fact that he fucked her when she was 15 seems on the face of it to be a fact.
The crux of all this is that what you say is only true if your definition of a fact is "anything that anyone ever says".
It's a while since I read through the various accounts given by LM and her friend Sable, but they are totally at odds one with another, to the extent that there is no real possibility of reading them all and having any confidence that any part of them is true. They can't possibly be 100% true because of all the contradictions. (Which, of course, is different from saying that no part of them can possibly be true.)
From memory, LM originally had the episode starting with her being picked out of the crowd at a Bowie concert at Long Beach in 1973 as a suitable shag for Bowie, by his bodyguard. Bowie and her (and, in some versions, Sable too) then arrange to have lunch the next day and spend the rest of the day on an extended date at various LA bars before going back to his hotel and spending all night together until they are woken by Angie Bowie the next morning.
The major problem with this tale is that Bowie actually performed at the Hollywood Palladium the day after the Long Beach concert, so it can't possibly have happened. I don't know if Lm became aware of this difficulty or what, but in later versions she starts the story two days earlier. She gets invited, either by word-of-mouth or by a phonecall from Bowie's people, on a date with Bowie, and the next day a limo comes to pick her up from her mum's house. At the end of the story, instead of being disturbed by Bowie's wife, Bowie gives her a thankyou gift of a handful of tickets to the concert where the story had started in the earlier version.
There's also the question of who Bowie had sex with. In some versions, it's just Lori, and in some Lori makes the charitable suggestion that Sable should join them. When Sable has told the story, it's Sable who has sex with Bowie and she has no idea where Lori has disappeared to. Sable's version also has a different beginning, where the girls sneak into Bowie's hotel to track him down.
There's various other issues with the stories, and I can't remember them all, but one is the claim that John Lennon and Yoko Ono popped in to see Bowie while he and Lori were eating in a restaurant. This seems unlikely because, according to other accounts, Bowie and Lennon only met for the first time a couple of years later. And there's another story told by Lori about her having sex with Mick Jagger when they both went to the recording sessions for a Ringo Starr album, but no-one else seems to remember Jagger having been present at these sessions.