User blog comment:Omega natsu2/Episode 176: The Dragon King, Review./@comment-209.89.93.78-20140408132554/@comment-209.89.93.78-20140411021643

The longest an opening has been used for is 12 episodes (Correct me if I'm wrong). Assuming each episodes animates 2 chapters, then the final episode where opening 15 is used will cover chapters 323 and 324 with 324 being... (SPOILER ALERT)

SPOILER ALERT

(SPOILER ALERT)...the chapter where Future Lucy dies, so the 16th opening might show Future Lucy's death and more of Future Rogue. Hopefully every single frame isn't a spoiler like opening 10 XD.