Hello, any query you make from Kamailio, you'll have to handle it yourself, so the
load will be affected, of course.
There are alternatives to use such as CGRates, or simply through reading JSON socket
events. Also, avoid performing any procedures within the B2BUA, whether it's
FreeSwitch or Asterisk. The more external your billing control is, the better performance
you can achieve. Here's some material for you to check out:
https://github.com/cgrates/cgrates
https://www.kamailio.org/events/2015-KamailioWorld/Day2/14-Dan.Bogos-Advanc…
https://www.youtube.com/watch?v=Hsvcwleb-fY&t=2s
This is my humble opinion, within what I can contribute ;).
regards