Is there any chance you can add a graphics card to your system ? It doesn't need to be anything fancy at all, just a cheap low profile one with 1 gig of gddr5 vram on it, shouldn't cost more than 30-40$.
It would help out quite a lot but in the meantime in BigBox try turning off all the transition effects and set your image quality to medium. There are some performance tips which may help you in this thread here if you haven't seen it already.
You shouldn't be getting freezes though, @Jason Carr has been testing BigBox on a GPD Win which is pretty low end hardware and aiming to get it running well with certain settings.