as per MS, concurrent Live events can be 15, when we produce Live events using Teams as well as using external App/device at the same time, will that increase to 15+15=30 or still will remain 15 only
As Stream Live Events is retired it's replaced by Teams Live Events. Currently the limit for Teams Live Events running concurrently is 50 no matter if it's a Teams produced, or Teams external encoder produced. See the "Important" note at the top of this page that changes the limit temporarily from 15 to 50. https://learn.microsoft.com/en-us/microsoftteams/teams-live-events/plan-for-teams-live-events#teams-...
The limit will apply to both encoder and non-encoder when Stream Live Events is retired.