After playing with my cube (
https://cubecobra.com/cube/list/df406254-a7ef-4db8-8674-428660fb2fc0) with friends, I made a few changes.
Replaced unmask and foil for the evoke elementals of the same color, they share a similar role but also are modal as they can be played as a good value 4 mana creature, often getting a 2for1 of sorts if timed correctly.
I felt there wasn't enough reason to pick the old free cards, but the new ones can be played in multiple ways, increasing player choice.
Another change I have made is replacing brainstorm with ancestral recall (remember you do not lose to decking). This is mostly because brainstorm felt a bit stale, but I still wanted Blue to have a way to see more of their resources sooner.
Ancestral recall is one of the most broken cards in the game in most formats, but in this 15-card deck format, I feel like it has actually reasonable trade-offs to playing it, as when drawn late, it does little.
Also, targeting your opponent with it can actually be a good play! Consider being on the play, having dropped a land and passed, and your opponent doing the same. At the end of their turn, you can force them to draw three, making them discard three cards to hand size, depriving them of those resources for the rest of the game!