@ModernThinker great suggestion... others I know had already done this, they said things got faster for a couple weeks then got bad again.
Anyway, I tried it... it works... my game (on a Nvidia Gaming tablet) was lagging so bad, I lost interest in playing the game. I deleted there entire game, rebooted, reinstalled, and eventually played until I could restore from facebook, and yes... SimCity is back to a playable game.
In effect the "delete the game" and reinstall, and then restore... means every single file on your (and now my) device is the current version of the game now.
But for this problem to happen at all... means the December update, 1 or more functions that used to be say in file1, file2, file3, sort of thing... were moved to file4, file5, file6... the developers however did not instruct the update to delete file1,2,3. Which means multiple versions of the same function existed because both the old - obsolete files were not deleted, and the new replacement files were a new name.
So as for you "kicking yourself"... I'd say, we all should get a round of kicking EA as their developers obviously have no idea how to properly maintain a game.
This also implies anytime EA puts out an update to this game, we may all need to delete the game and reinstall each and every time. sigh.
Anyway, thanks again for recommendation. I've passed it on to my club in general, a few people I have also on facebook in my club, said the whole app hasn't even finished loading for 3 days now, so I'll just tell them to delete and try reinstall.