If you're experiencing slowness with the Panorama GUI, the first area to look at is the underlying configuration of VMware. The VM host requires a high-speed disk and fast CPUs, preferably on dedicated hardware to ensure that other images aren’t consuming the CPU or I/O channel. Examining the VMware statistics will help determine if any particular resource is being maxed out (disk I/O, Processor, memory, and so on).
Note: A minimum of 4GB RAM and 4 processor cores is required for deployments with up to 10 managed firewalls. For more managed firewalls it is required to have 8 processor cores and 8GB to 16GB or RAM. Check here for more system requirements
Other factors that might cause GUI slowness:
Too many log messages being sent to the system. Use the command "debug log-collector log-collection-stats show incoming-logs " to check the logging rate if the panorama is in panorama mode acting as log-collector as well. You can skip this if the panorama is in management-only mode.
Changes being made while a report is running. Check the configuration logs of the panorama when the report is running.
More than one administrator committing changes at the same time. Check show jobs all to find the commit jobs running on the panorama.
Slowness of the user's computer, or a slow link to Panorama. You can try accessing Panorama from a different system or a host in the same subnet as the Panorama to figure out link or host issues.