Why is prezi so laggy?

The top cause for this is a slow computer that is struggling to run the Prezi and all the other stuff and apps that you may have open. This is true for Prezi in a browser too.

Try this:
Restart your laptop or computer and then run ONLY the Prezi Desktop App and play a Prezi or a Prezi Video. If the presentation isn’t laggy (or noticeably less laggy,) then maybe you need a computer update.