Future episode titiles and a few info from Megami Magazine.
Spoiler:
14 「最強VS最弱（さいきょうさいじゃく）」 The strongest VS the weakest (the strongest and the weakest)
15 「御使墜し（エンゼルフォール） Angel fall
16 「父親（かみじょうとうや）」 Father (Kamijyou Touya)
The article says the highlight of the episode 15 is "Index" 's one piece and Microkini.
Accelerator arc seems to continue the episode 14 so second OP/ED might start from the episode 15.