Event time interval parameters

Hi
Is there a specific set of parameters in one of the .js files to alter to allow 15 minute intervals when creating an event?
Obviously everything is set to 30 minute intervals at present as default but it is not fine enough for me to match the display for the user simply by entering the start and finish times elsewhere.
Can this either be updated or a clue given as to what to alter for customisation?
Thank you in advance.
AOC