If you are suffered by accessing shared folders too slow, try this:
1. if your vm is running Windows,
2. if your share folder name is like that : “\vboxsvr\<share fodler>”
3. if you install windows in disk c of your vm
4. please modify c:\windows\system32\drivers\etc\hosts
5. modify the line “127.0.0.1 localhost” to “127.0.0.1 localhost vboxsvr”
6. reboot vm, and you can see there’s a lot of improvement.
Made an incredible difference for me.