Just checked, it is 10 people per group, still doesn't help you with your situation:
Group Paging
Group Paging directs Speakerphone Paging either to a selected group of extensions, such as a
department or work area, or to all extensions in the system, except QCC operator positions.
The system automatically reserves extension numbers 793 through 798 for the first six
speakerphone Paging Groups. Up to 10 extensions can be assigned to each speakerphone
Paging Group. The seventh speakerphone Paging Group is called the Page All group and is
factory-set to page all extension numbers. The system automatically reserves extension number
799 for the Page All group. An extension can belong to up to seven speakerphone Paging Groups
(including the Page All group).