
Even in the datasheet to Skype Business video calling they don't offer more than 10 people option...
And here are the system requirements:
"System requirements
Group video calls can be between three or more people (up to a max. of 10), and at least one person on the call needs a group video
calling subscription. For the best quality, we currently recommend video calls with up to five people.
For group video calls with three people, we recommend a minimum connection of 2Mbps downlink, a Core 2 Duo 1.8 GHz CPU,
a 128MB RAM, DirectX 9.0c (min) graphics card and 1GB of memory.
For group video calls with five people, we recommend a minimum connection of 4Mbps downlink, a Core 2 Duo 2.8 GHz CPU,
a 128MB RAM, DirectX 9.0c (min) graphics card and 1GB of memory.
For group video calls with 7 or more people, we recommend a minimum connection of 8Mbps downlink, an Intel i7 CPU,
a 256MB RAM, DirectX 9.0c (min) graphics card and 2GB of memory.
"
And... the 25 people that can attend means voice-only conference, no video...
Not sure it will be necessary this time, but if you have more than 8-10 once, maybe Google hangout or other video conference call software will be a better choice...
[added:] You can
record the video chat if you like
.
Andrea