Very slow file copy to encrypted disk image I have a new iMac running El Capitan.  Bought a SanDisk flash drive for backup.  I created an encrypted disk image on the flash drive.

Here's the problem:  copying 10GB to the unencrypted part of the flash drive takes about 5-6 minutes.  Copying the same 10GB to the encrypted disk image is estimated to take 2 hours.

Why the huge difference in copy times?  Is there any way to speed up file copying to an encrypted disk image?
Finder needs to encrypt each file before copying it to the disk. 

No, there is not a way to speed it up without removing drive encryption.