Why is my Windows 10 Pro USB Legacy boot Slow

[KINGSLAYER THE 3RD]

I a while ago i installed windows 10 Pro on my Usb 3.0 External HDD and when i installed it and then booted using legacy i get very slow hard performances which makes the whole system slow basics task only using 2.2 mbs and it using 100% of the Disk PLS Help TY