I have an Sandisk UltraFit 256GB USB drive formatted with exFat connected to one USB3 port on my MacBook Air mid 2012. Though it seems to relocate, the relocation seems to go incredibly slow. Any ideas?

I have an Sandisk UltraFit 256GB USB drive formatted with exFat connected to one USB3 port on my MacBook Air mid 2012. Though it seems to relocate, the relocation seems to go incredibly slow. Since I have several reasons for using it on Windows also, for instance parts of my GoPro import and editing has to be done on Windows, I use exFat. After 12 hours it had only moved 17 GB of 65. Is exFat slower? It did not take especially long to move about 80 GB from my old Sandisk UltraFit 128 exFat to the new 256 GB UltraFit on the same Mac. Ideas?