World Lagging

I have been working on a world for almost six months with my friend, and as of a few weeks ago there has been significant delay for every action. For instance, when mining, the blocks don't break at first, chests don't open until you repeatedly click, and the animals and other players jump from one place to another. This makes it difficult to play properly as it is hard to interact with things, especially those which involve movement. We have tried entering other worlds, and they work fine. We've also made a copy of this world, and the issue persists. Is there any way of fixing this?