There is a ‘Delay the effect of this rule by this many minutes’ setting that you could use for the 15 minute delay. Setup a trigger for when the garage door is open. The action would be to close the door and delay by 15 minutes. Under more options select ‘Only during a certain time’ or ‘Only when mode is’
I believe this will only work if the door is opened during the time window. If you wanted this to always work you could use a rule to evaluate the time or mode change as well as the door state and then delay the action.
Also make sure you are using the most recent version ‘Rule Machine with Triggers’