WordCamp Central has made public some statistics of WordCamps that occurred in 2015. Among the highlights: WordCamps were held in 34 different countries with over 600 organizers (nearly half of those first time organizers) and over unique 1670 speakers.
This was the first year for WordCamp US (which, not surprisingly, had the most speakers of any WordCamp). WordCamps are gradually increasing in both quantity and attendance, so it should be interesting to see 2016's numbers this time next year. I know WordCamp Europe will be even bigger than WordCamp US, with over 2,200 attendees.