You can find very usefull info at https://live.paloaltonetworks.com/t5/Management-Articles/Graphic-Traffic-Monitoring-for-Interfaces-Q...
Look at the bottom for long time graph
The firewall doesn't save historic reports. You'll need to contact your SE for a feature request. In the meantime scripting can help you out. You can found some of them in the API section and I'm not sure if the panchrome extension has historic reports for QoS.
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