How do you spell time specifications given in (military) "Zulu time"?

For an example, let's consider the time specification "1539Z".

How do the people in the military spell that? "Fifteen thirty-nine Zulu"? "Fifteen thirty-nine zee"? "One fife tree niner zulu"? Are there differences between US, Canadian, British, Australian (and other English-speaking NATO members) spelling of this time specification - and if so, what are they?

The scenario here is how to put the time in writing as direct speech/quotation of someone. This is important in the following cases:

• It's a direct quotation, and I want to write down what would be spoken exactly as it would be spoken (but don't have access to audio logs).
• It's direct speech in a work of fiction, where how someone spells the time specification gives a hint to their background.

NATO military pronounces individual letters as words to ensure clarity. They use the NATO Phonetic alphabet. Time is pronounced as two digit/two digit, unless it's precisely on the hour. 0430 is oh-four thirty, or zero-four thirty. 21:35 is twenty-one thirty-five. 19:00 is nineteen hundred.

Thus 1539Z "Fifteen thirty-nine Zulu"

As an aside, Zulu represents Greenwich Mean Time.