Large MC Windows 10 world, near 100% CPU

I have a Windows 10 laptop with Minecraft Windows 10 Edition v1.0.4. When I play some worlds or in a Realm, Minecraft responds pretty well. But I have a Survival world that is 104.6 MB. (I am trying to get all the achievements, and I had to explore a bit to get cactus and cocoa beans.)

When I open that world, there is a lot of lag. The CPU in task manager goes near 100%. I am trying to kill the Enderdragon now and it's not that easy. I've turned down most of the video settings (except I need a little render distance so I can see which towers I have to take out).