At the moment we skip these two tests: 
-k "not (TestCopyoffload2TbVmSnapshotsMigration or TestCopyoffloadLargeVmMigration)"
 
As we now fill the disk, it takes too long to fill in these large disks with 50% maybe with 20% is faster but still takes too long. Once the disks are filled the migration part also takes longer. 

One possible idea is for these test create a secondary source image, already filled with random data cutting the test tine in half. 
Another option run these scale test on a separate job once a week. 

With the latest source image and fastest fill method ~300-265 MB/s,  a 1TB disk would take about an hour just to create/fill the source VM.