16:15 is spoken as:
12 hour clock: four fifteen pm, quarter past four pm, fifteen minutes past four pm, three quarters to five pm, fourty-five minutes to five pm
24 hour clock: sixteen fifteen, quarter past sixteen, fifteen minutes past sixteen, three quarters to seventeen, fourty-five minutes to seventeen
Military: one-six-one-five hours, sixteen fifteen hours

^* This conversion is correct for the 2016 Rio Olympic Games ( because time difference between your local time and Rio time now is hour(s) and in August 2016 is hour(s) )
This time conversion is valid now. Due to DST (Daylight Saving Time) changes it could not be correct for any date in the year. For example: if you check the time in summer, it could NOT be correct in winter.