These take place every two years in the alternate year to the World Championships
2018 - Riva Del Garda
on the Zuider Zee in The Netherlands
2014 - Porta Pollença, Mallorca, Spain
The RCNPP (Real Club Náutic de Port de Pollença) ran the Flying Fifteen Championship 2014 in Port de Pollensa on Mallorca, Spain, between 14th and 19th of September 2014.
2012 - Riva del Garda, Italy
In 2012 the Flying 15s travelled to Italy and Riva Del Garda, where the Championships were organised by the Fraglia Vela Riva.
You can see photos of the event here, a video here and read the race report here.