if I memba correctly they reran the 15 event like right before endwalker dropt so we could guess they'll drop it again in 6.55.
Course I think a smarter idea would be to make it the first event of 7.0 like a week or two after 7.0 drops when everyones playing like daily and actively.
Course I would prefer if they upgraded the event and maybe added Noctis' timeskip outfit as new rewards from that one FATE or added glamour weapons.