Not only Wikipedia is turning 15 this year. The FSFE will celebrate its decade-and-a-half long existence at its Berlin summit this September.
They have very warmly invited us to participate and to submit sessions.  The deadline, however, is pretty soon (17 May).
I myself will propose something policy related, as they are also pushing the free agenda in Brussels and we can coordinate much better on this.
Please don't hesitate to share this call on other mailing lists, as I will only do so here.