Why is prezi so slow?

Is it? I would agree with you if we were talking about Prezi Classic, which was based on an old piece of technology called Flash. However, modern versions of Prezi are based on HTML5 and have far fewer issues than its Flash-based old-brother.

Prezi Next, created using the programming language HTML5, is much more lightweight than Prezi Classic and can support larger and heavier presentations with the same resources (CPU, RAM, etc.)

Factors like the connection’s speed, computing power, and resource-charing will impact Prezi’s speed.

I get to help hundreds of executives to adopt Prezi; in 99% of the cases, the culprit is either old computers or slow Internet.