Performance/FPS rate gradually goes down when generating or creating worlds on my device

When I am in a world or newly created world, FPS on my device gradually goes down. If I don't move and look down or up, FPS rises and will not lag, but If i look around while moving, the frames will start going down and will reach to the lowest FPS, lower than 20.0 or 10.0. I am using a different device which is a tablet (ASUS Nexus 7). The other device I use is my phone (Vivo 1606), the one that I use to report bugs. Flat words are unaffected. This only occurs on my device. Even if I put my render distance to the lowest chunk , the game will always lag. Also, the memory of this device (ASUS Nexus 7) is not even close to being maxed out. It lags anywhere I move, not only near beaches, but if I am fully submerged in water, FPS also rises and my games doesn't lag unless if I am out of water or wandering around.