The capacity for dynamic addresses on the pa-820 according to this article is 1000 https://docs.paloaltonetworks.com/pan-os/8-1/pan-os-admin/policy/monitor-changes-in-the-virtual-envi...
But that seems to be a little out of the 2500 that your commit error has which is the limit of the 850, hope that helps a little at least.
Are you managing this directly or through Panorama? Panorama by default will attempt to sync all shared objects to a firewall even if they aren't being utilized in policy on that device. You can modify this by clearing the Share Unused Address and Service Objects with Devices option so that only shared objects that are actually referenced are being pushed.
If you are managing this locally directly on the firewall then I would do the following:
The article that you mentioned is very specific to DAG IP addresses and not actual address objects, where the 820 can have 2,500.
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