On SMC 2.0 V600R006C10SPC900, conferences end rather quick (approx. 2 minutes) after the last participant quits. This behavior appears only after an upgrade to this version - it was not present on the version before upgrade (V600R006C10SPC300).
Verified the parameter "Time to termination after last participant leaves the conference" (under “System -> Settings -> Conference”), but this parameter had a high value (750 min).
There is another newly added parameter, "Duration for retaining disconnected dynamic participant" (under “System -> Settings -> Conference”), that did not exist in the previous versions. This parameter only affects the participants that dynamically join a conference. This parameter has the default value of 120 seconds.
The parameter "Time to termination after last participant leaves the conference" is now referring only to the participants staticly added when you schedule a conference.
Increase the value of parameter "Duration for retaining disconnected dynamic participant" to maximum value: 300 seconds.