The 7815 supports a maximum of 200 phones, and only a 2-server cluster (primary and backup) is supported with this server. So no, you cannot use the 7815 to support 800 users.
Here's an excerpt from the product catalog:
"The Cisco Media Convergence Server 7815-1000 (MCS 7815-1000) is the platform designed to address the needs of locations requiring 200 IP phones or less. The MCS 7815-1000 can be configured to provide N+1 redundancy for a location through the installation of a second MCS 7815-1000 acting as a hot-standby server. "
SIP traces provide key information in troubleshooting SIP Trunks, SIP
endpoints and other SIP related issues. Even though these traces are in
clear text, these texts can be gibberish unless you understand fully
what they mean. This document attempts to br...
Please find the attached HTML document, download and open it on your PC.
This provides an easy to use form where you simply answer a few
questions and it will render the proper jabber-config.xml file for you
to copy/paste. There is built in logic to verif...
CUCM Database Replication is an area in which Cisco customers and
partners have asked for more in-depth training in being able to properly
assess a replication problem and potentially resolve an issue without
involving TAC. This document discusses the bas...