Why not just host an invite only session, add one person at a time & drop cash.. When another wants to be added, invite them and kick the other player?
Having a full lobby of people to do a cash drop is idiotic.. People will get bored of waiting for others to get "10-15mill".
People going to either loot the drop or spam you with "me next".
Not to mention you've then got to manage all 15 people in one sitting.