I have a Vivo y11 smartphone with 512mb ram. I know it is not sufficient to run Pokemon go, but still I want it. It crashes down every time.
This game is new and maybe contains alot of bugs and errors.
Make sure you disable, Mobile Data when you are not outside and you have access to WIFI. Two connection at same times will freeze/crash the game.
An other thing is to deactive the Camera when you catch or battle something because this sometimes causes crashes if you do something wrong.
People say it also depends on the country because of the Pokemon GO Servers
Make sure you are not far away from a pokemon stop, pokemon arena or pokemon while using them or contacting them, because if you move far away you can't catch it anymore and this causes crashes if something didn't went good.
If it crashes you should try to click the button again until it works, and if you have problems at the starting you have to reinstall it.