1) It absolutely shouldn't do that, please download from my mega reposidory I've set up (just click download here on itch)
2) Are you playing the latest available version? If so, then the lagginess is probably due to your phone being out of date or something like that - first time I'm hearing about optimisation problems, nobody has said a thing thus far. I've certainly tested it myself and the optimisation is fine and I have a fairly old phone myself so I really don't know if the fault lies with me.
Consider playing on an emulator for a better experience.
3)Backward feature exists, the quick menu to the left on the screen has it - just click "back". It should go backwards with the dialogue for you