I use 24h in speech, it trips up some people a little but they all understand and I've gotten a few to switch!

My native language is Dutch, but I to give an example I say “vijftien uur” for 15:00 / 3pm and “vijtien uur dertig” for 15:30 / 3:30pm. My closest English equivalents would be “fifteen oʼclocm” and “fifteen thirty”, really.

My point is, make the tiniest possible step, only replace the number of the hour with the 24h variant and drop the am/pm part.