Try changing the Graphics settings to "Conserve Memory" in the preferences.
I'm playing the game as well on a tablet, with enough power, but neither of the 3 graphics options make the game less laggy. I'm assuming it's because Python in Ren'py is being used which is a bit slow in general compared to compiled languages?
In the next version (which will come in a few days), there will be an option to disable power save in the settings menu.
For now, try playing the game while charging your tablet and see if that helps.
