Do a full installation without removing the current installation and that will fix it.
There may be a couple of reasons why this happens.
1) Running the game off of an SSD.
2) Low space on drive C:.
3) Low memory available in the computer. (Superfetch service can cause this)
4) Running any anti-xxxx software.
5) Running the download over a wireless connection.
There may be others, but those come to mind as being the most prolific.