Why do you need to transfer files?
Are you making a copy? Or did you try to move the files?
Poor transfer speed like yu describe, where it slows down at the end, may indicate a hardware issue.
Here is a link that might relate to your problem:
https://www.justanswer.com/computer/6ros7-hear-hard-drive-speed-slow-down-speed.htmlHe was told that it is normal, then he wrote back:
This is NOT normal! Have had this computor for over 10 years before replacing the first hard drive. First hard drive did the same, I would hear it speed up and stay at that loud speed, got very loud, that's why I replaced it. Friend said the hard drive was going . Never got this loud of sound before, and on graphic games will cause a lot of lag and sometimes freeze up the computer.
Does that sound like your problem?
My suggestion is this; Get an exact replacement for the hard drive and make a 'clone' of the original drive. Then swap out with the new drive. If I am right,that will speed up your hard drive transfer speeds.
I hope this helps.
Here is one of the free programs I like:
https://www.easeus.com/The free version is good enough.