FileVault Stuck on Pause
I asked after this while attending WWDC 2015 and was told that the "Encryption Paused" issue was addressed in 10.10.3. 

The root cause was a problem with resizing the CoreStorage volume during the encryption process. When the CoreStorage volume was unable to grow, the encryption was paused and could not resume until the resize issue was addressed.

To fix this issue:


Update your Mac to 10.10.3 or boot from an alternate drive which is running 10.10.3.
Unlock the encrypted drive if necessary
Open Terminal
Run the following command to get your Mac's disk identifier:

diskutil list

Once you have the disk identifier information, run the following command with root privileges:

fsck_cs -y disk_identifier_goes_here

fsck_cs should repair the CoreStorage volume and address the resizing issue. As part of the output, it should show that encryption is resuming.