If you use your USB flash drive only with Macs, you may be able to increase its speed by changing its format to Mac OS. Just like any other drive, flash drives can be formatted for use on either Windows or Macs, and almost always arrive formatted for Windows. (Macs can read Windows-formatted drives, but Windows requires a third-party utility to read a Mac-formatted drive.)
You can use Apple’s Disk Utility (in Applications:Utilities) to reformat the drive for Macs. Under the Erase tab, choose Mac os Extended from the Volume Format pop-up menu. You can also give it a name - using your phone number is a good option in case you lose it. When you click the Erase button, all the data on the drive will be erased and the drive will be formatted for Mac OS.
The next time you copy files to or from the drive, you should see a speed improvement.