When I open KMZ files it takes several minutes, but when I load their non-compressed equivalent KML file it's instantaneous.
I have attached a 7MB KMZ which illustrates the problem. This file takes several minutes on my computer to open, but when I unzip it and use the internal `doc.kml` file directly it takes seconds. I have other KMZ files which exhibit similar delays in opening.
As a way of benchmarking, Google Earth loads both the KMZ and the KML in just a few seconds.
The KMZ is a very simple hierarchy of NetworkLink tags and associated image tiles.
P.S. The attached file had to have `.zip` appended to its name in order to upload to the site. Simply remove the `.zip` and it will function like a normal KMZ file. (And for those not familiar, decompress any KMZ to turn it into a KML.)