I have a HP 620 laptop with a "Realtek PCIe FE Family Controller"

I have 70 of these units to image and image upload take 30min. which is pretty standard for this image size. However image download to other HP 620 laptops take over 280min.! Does anyone else have this problem? Other images, for desktop and different laptops, from this image server have no issues, we have also recreated the image, uploaded it and attempted another download with the same results. Please advise.