Any chance you would be able to email me (share a private link to some kind of onedrive) what you have in the env where you import and the import file you are uploading? I would profile the operation to find out the bottleneck. (jan.blaha@jsreport.net)
At this moment, you should be able to prepare separate blob storage and when you are confident, switch the production env to it.
The problem with blob storage is that it is significantly slower to work with than a DB or file system. We need to perform many small operations, which are slow in total. This driver was implemented 10 years ago, because there were no other simple options. Nowadays, you can share a managed disk or Azure Files, which provides better performance in this case. This is just to clarify the poor performance on big imports with azure storage.