Game lags on ios devices and wont open after first time opening on older ios devices such as the 11.

I have a game that lags on ios devices. Its a game where cars spawn and you walk across a long road to avoid getting hit and when u reach the end you spawn back at the beggining. The game does have one source of movable light. I dont use post process. And most of my stastic meshes are very high poly. It can be alot of cars in the street at one time however. I was wondering what settings should I defenetly change so my game perofrms well on mobile. Also after playing the game once on my iphone 11. I cant open the game once I try to close app and go back in. I get to the play menu, but once I try to load up the game it closes me out the app. Is this also due to something with lag or performance issues?