Your -q15m is like -q30m.
Process saved messages in the queue at given intervals. If time
is omitted, process the queue once. Time is given as a tagged
number, with 's' being seconds, 'm' being minutes (default), 'h'
being hours, 'd' being days, and 'w' being weeks. For example,
'-q1h30m' or '-q90m' would both set the timeout to one hour
thirty minutes. By default, sendmail will run in the back-
ground. This option can be used safely with -bd.