The game has a lot of elements simulating at once, so it is pretty intense on the processor, and we like to run at as high a frame rate as possible. However, there is a "Battery Saver" option in the settings panel, which you can open up from the gear icon on the World Map. Choose Battery Life.
>The dialog will let you choose between high performance or better battery life. So you can choose to save some battery, and the game will lock itself to a cap of 30 FPS, which may make it look choppy, or maybe it will look completely fine to you -- different players have different sensitivity to frame rate. You can give it a try. Your mileage may vary depending on your particular device. Hope that helps! Happy Merging!