Serious lag issues happening every time I spawn a dolphin or turtle.

I'm on pe, and every time I build an aquarium, and spawn dolphins and turtles, my whole world suddenly gets really buggy and laggy. Animals and normally moving things stay in place for 15 seconds per 30 seconds. I've tried spawning them in on both Creative and Survival, but same result with both. It's happened now on 5 of my worlds, and even when I destroyed the aquarium, there's still massive lag. Really annoying, and also quite a pain, as I'm a softy for dolphins and was hoping to have a nice aquarium filled with some.