18-25 seconds during calls? As in the speech-to-speech latency is 18-25 seconds? The first thing would be to understand what is introducing that delay, and my guess is it would be multiple things. I’m still working on a better resource for this, but a good place to start is this FAQ: Frequently Asked Questions (FAQ) - #13 by darryncampbell
I recommend first eliminating the SIP leg, to measure your latency when connecting to the room through the web. Then understand what the latency is in your SIP leg by looking at your PCAP files (does the call involve multiple trans-atlantic hops for example)