Services cost money to run. Clearly this service delivered value to you and your group. You could have just asked everyone to donate $0.25+ at each meetup to ke

Services cost money to run. Clearly this service delivered value to you and your group. You could have just asked everyone to donate $0.25+ at each meetup to keep it going. $15 is very reasonable, especially because IoT has many business/professional facets to it, so the group could be augmenting people's careers.