Not really true either, it's often called military time as a colloquialism because people will know what you mean and it strangely feels more normal/easier to say than "Twenty Four Hour Clock."

EDIT: Also for the nomenclature, I personally still refer to time in the 12 hr format when talking, but if for some reason I have to say the 24 hr format it depends on the number. I would also say fifteen thirty for 15:30, but I would say fifteen hundred for 15:00.