Greetings Rahuf,

Good catch that the "Created" condition. Because it says "relative before 15 days ago" it is not looking for Created IS 15 days ago, it is looking for Created >= 15 days ago. This means it will return results that are 16 days, 17 days, 18 days, etc. On my PDI, I changed "relative" to "on" but unfortunately, I did NOT see the option to pick 15 days exactly. What you may want to do is use an in-line script and call the GlideDateTime API. You can use the .addDays method and use a negative number to subtract the days. 

Here is a screenshot from the ServiceNow Developer website.