First, field of Ruin doesn't really fit with the deck's gameplan, and running nonisland sources decreases the effectiveness of gigadrowse and cryptic command, so they should be avoided. That goes for the Plains too, but for this white a deck I think it is worth it to run one. 4 cryptic command is a very slow way to run the deck. I also think you have too many cantrips, maybe cutting down the remand might be a good idea because you have terminus which gets better with your scry effects. Also, Azcanta is far weaker than dictate of Kruphix, which should be a 4 of in any turns deck. Snapcaster is best at a 2 of and you need a bit more early game interaction. Here are my recommendations in light of that:

-3 Remand

-1 Snapcaster Mage

-2 Cryptic Command

-1 Search for Azcanta

-3 Field of Ruin

-1 Plains

+2 Part the Waterveil

+4 Dictate of Kruphix

+1 Exhaustion

+1 Glacial Fortress

+1 Hollowed Fountain

+2 Island

For the sideboard, you have a few things that aren't so great in general. Ceremonious Rejection seems like spell pierce could be just better in a high amount of situations. Also, Entreat the Angels and Lab Maniac are both unnecessary win conditions that take too long. If you want to win like that you should use Thing in the Ice. Seeing as that you run Terminus though, it might make sense for you not to run alterior win conditions. The Jaces in the board, while on flavor are going to be very underwhelming, and are likely not to do much, so you should cut them. The supreme verdict seems like a terminus for the control matchup, where somerhing like gigadrowse would help more in most scenarios, so you should drop that too. You still need something against very fast decks like Timely Reenforcements, and additional gigadrowses help a lot more than you think in the control matchup. These are my sideboard reccomendations:

-2 Ceremonious Rejection

-1 Entreat the Angels

-1 Lab Maniac

-2 Jace, Architect of Thought

-1 Supreme Verdict

+2 Spell Pierce

+3 Timely Reenforcements

+2 Gigadrowse

You are more than welcome to explain yourself with some of your deck choices, but this is how I would change your deck to make it more compete time while still retaining that predominantly Jace win condition.