
In apex, By default scheduled job run in every 1 hour using CRON expression but you can scheduled this job in every 5 minutes or 10 minutes duration.

System.Schedulable interface has on method which we need to implement inside our apex class and this is the method which will execute every interval our class is scheduled for.
From execute method we do either call our Batch Apex or Our Simple Apex Class Method.

If you wanted to schedule your batch job for every 15 minutes use below cron expression