Hi,
as r.sander wrote, you need to configure the rule “maximum number of check attempts” to 15.
If you use a plugin or a local script you will be able to start the code in x minutes. The only thing you need ist to create a directory e.g. check_mk_agent/local/900, out your code in there and the sript will run every 15 Minutes. One big effort is, that the output is also cached.
Regards,
Christian