This is better fit for the Suggestions section.
Also are you sure you aren't the one lagging, and not the server?
1)In Pika, press F3 (A key that should be on the very top of your keyboard)
After that you will see a your screen covered in text. Look for the line of text that says FPS (Frames per second) check what number it is. If it is low (3-30) then your hardware is bad and can't support Minecraft. You could try lowering the graphics in the Video Settings or install Optifine.
2)Go to a internet speed test site and check you internet speed. If you have low download or upload speed your internet isn't very good. If you have high ping your internet isn't very good.
You could get a better connection by getting an ethernet cable or investing more money into speed for your router.
3) Ask in chat is anyone else lagging.
If they are, then Pika must be lagging. This happens when there are lots of players online or lots of entities have spawned.
There isn't anything you can do here, and Pika can't do anything here either, since the Host of Pika decides the max capabilities of Pika.