I installed Minecraft PE v1.4 and it is lagging hard at max graphics btw i am playing from iphone 7 plus, i tried at lower settings but when the chunks have loaded it lagged again
Does it lag when you set the graphics settings to the absolute minimum?
Is your phone downloading stuff or installing updates in the background? Is your phone jailbroken? Does restarting your phone help?
Perhaps it's your world seed. If you make a new world, does it still lag?
It is lagging between 20 and 32 chunks but when i put on 16 is working fine, not the best .