Dear Tim OBriant,
Thanks for posting in Microsoft community. We are glad to help you.
We understand the uploading process are slow with big files on your side. Basically the speed depends on the internet environment and the Microsoft server location. You may have a try with the following work around and see if this could be faster:
1.Create a short cut of the SharePoint to OneDrive for Business: Add shortcuts to shared folders in OneDrive for work or school - Microsoft Support
2.Upload the files in your local OneDrive sync folder(The shortcut folder): Sync files with OneDrive in Windows - Microsoft Support
3.Check if the speed would be faster or not.
If the speed of the uploading process is still slow, we're afraid this issue may need to check the environment on your side for further investigation.
As forum support we may not have enough permission and resource to directly check the environment on your side.
We notice you post this question in For business category, so we suppose you have Microsoft 365 for business subscription. In this situation, we sincerely recommend you contact your Microsoft 365 administrator, follow steps in this article and try to create a support ticket to contact Online Support. The support team over there has higher permission than us, they can remotely help check the situation on your side, involve more resource to collect logs and help you do troubleshooting. This would be a more efficient way in handling this case for you.
For reference: How do I find my Microsoft 365 admin?
Thanks for your understanding and cooperation! Have a good day.
Sincerely,
Sean | Microsoft Community Moderator