Given that the 15 year old female will be very obviously female this could be very upsetting for some men as well as putting the female in danger.
How to predict how a man who is distressed or embarrassed by this invasion of his privacy might react in these circumstances? Some might get aggressive. Others, as reported in an earlier thread (someone else might remember where to find it) would act protectively.
In the incident mentioned in a previous thread, a young teenager presented herself at the urinal next to a man and inserted a She-Wee into her trousers. IIRC the man took his time washing his hands to make sure she was safe until she left. I think this was daytime in a town toilet rather than a nightclub, which is a more likely setting for socially transgressive behaviour.
This sort of behaviour by young females is both risky and profoundly disrespectful, just as disrespectful as men using The Ladies. That applies whether the girl/woman is using a urinal in The Gents because she thinks she is a boy/man or because there is a long queue for The Ladies.
I hold my hand up and confess that I have occasionally dived into a cubicle in an unoccupied Gents Toilets in desperation but it takes things to a different level to stroll up next to a strange man using the urinals and nonchalantly whip out a SheWee.
If a man might be prosecuted under the Public Order Act 1986 for causing distress to women, by entering The Ladies and rummaging in his flies in full view of any woman present, then there should be no reason why an obvious female should not be prosecuted for doing the same in The Gents.
^www.legislation.gov.uk/ukpga/1986/64/section/5^
I think many (most?) people, male and female, would not regard it as a sign of “bigotry” (yawn) to suggest that a girl/young woman routinely using public urinals might be deserving of compassion and in need of psychological help, rather than applause for “bravery”.
I don’t disagree with some of your points, but I still believe most FtM individuals will prefer to use the toilet of their chosen sex.
My point was that it’s not so much that ‘some people suggest’ they should use these spaces as the fact that they themselves want to use them.