CDR logs call every 15 seconds instead of total

Hi all,

I'm using asterisk & FreePBX in 3 locations. one of the PBX's CDR module writes a active call in each 15 seconds.
So for each call i have 20-100 rows.
For example:

Pasted image1567x161 7.25 KB

Why does it happen and how i can fix it?

Thanks in advance!