Wait for guaranteed.  You got shafted... the other 3 epics guaranteed?  😆 

I need Keerya to finish Mikage.  I need Delaaja to fuse Keerya.  One of those two champs and I get Mikage.  

I'd 100% not bother with trying to get Keerya. It's not an X2 event, and even if you do happen to pull a lego, your odds are still quite low.

Delaaja is definitely more tempting. I think I'd definitely be tempted to use a few yellows to get her. Your odds are still quite low of course, but given a yellow is a guaranteed epic, and that there's about 225 epics, on the initial X15 you're at ~15/225 ~= 7%, then on the X20 you're at ~9%, and on X25 you're at ~12%. Still far from guaranteed, so it's up to you if you want to spend a few yellows to roll the dice, or wait until you get another guaranteed event, which could take who knows how long.

Since they the other 3 epics, I'd bet there will be a guarantee for Delaaja sometime soon.