Well, you are not meant doing them alone, although red one is easier to solo since its burst target single/double kami.

15 ap are only for materials to host expert and tickets. I don't think I saw them dropping cores.
Just wanted to give him 1 round dmg and thought 1,1k is ok...and got the shock in the 2nd round^^ Plus no one joins if you are waiting... 1 person min 52 and no hp missing... (maybe it was to late) So its hard to start a dungeon as a noobie and without guide help.

Dont know if soloing is even worth.

Drops seem ok (but it seems that it is much harder to get the SSR E. and Weapon compared with the normal Event).
Had the chance to join ragnarok a moment ago (30% left). I just made bursttime fullcombo, all skills 2 atk rounds and got 11 drops (2cores 9 mixed Tickets. Since i dont know what the others got i cannot compare).