Dag scheduler interval not working

Hello,

I have dag:

default_args = {
‘owner’: ‘jf’,
‘depends_on_past’: False
}

dag = DAG(‘hello_world’, description=‘Simple DAG’,

      start_date= datetime(2020, 1, 1, tzinfo=local_tz),  
      schedule_interval= '5 8 15 * *',   
      default_args = default_args, catchup=True)

For example:

Today is 15 day of month 8:00 AM. If I set schedule_interval= ‘5 8 * * *’ and run dag. Everything is OK. But if set set schedule_interval= ‘5 8 15 * *’ , dag doesn´t execute. Why?

Thank you for your answer.

Jakub