Nextcloud is amazing. Nextcloud Talk is amazing. Running all that through your basic NextCloud installation is a lot to require. So, you can leverage my Nextcloud Talk High Performance Backend. It includes access to my STUN and TURN server.
This will allow you to scale to “dozens” of users on your audio and video calls. We have servers in California and Germany.
The cost is $4/server/month, billed monthly, and subject to my reasonableness. Just reach out to email@example.com to get started!