A governance simulation would be most effective. 4-6 people participate, the rest is fishbowling the simulation. But I find it hard to do it in 90 minutes - especially if people want to also hear a little more about what Holacracy is. There is a lot to be explained. Also, for a simulation you need to have access to prepared simulation materials (or invent one yourself). For this slot I would probably rather go for a straight-up presentation and leave ample space for Q& A.