HP Deskjet 6122 Color Inkjet Printer - Manual (Page 126)

two-sided documents are printing
Printing two-sided documents takes more time than printing single-sided documents.
printer driver is outdated
An outdated printer driver may be installed.
For information about updating the printer driver, visit HP's Website at:
http://www.hp.com/go/mac-connect
computer does not meet system requirements
1. Verify that the computer's hard disk space or RAM meet system requirements.
For more information, see system requirements .
2. Increase free space on the hard drive.
If your computer does not have enough RAM, or a large amount of free space
on the hard drive, the printer processing time will be longer.