Update: I re-installed the game again, being careful to download everything before playing (disabled background download). The download all button says the Data is up do date, but oddly, game still downloads some stuff in some screens, like summoning characters for the first time. I tweaked a ton of options in my phone and some developer stuff, and still got lag.

Then I installed the JP version. 0 lag.

I guess it's gumicode, or the JP version has some tweaks that the GL version will get waaayyyy later. The lag seems related to memory/file access, it lags whenever it has to load something, Models, Effects, Animations, etc. For example, in the character equip screen I can see each item being loaded one by one.

Will still play it, the lag is very annoying, tough =/