Rule of thumb : Ripping speed should be at least twice burning speed.
Have you checked the ripping speed ? I think Nero has some facility in it to be able to check the read speed.
As the last poster said, use the fastest reader/ripper as the source..
I dont think 15 mins is unreasonable for a disk-disk copy.
As for the HDD image to the 3 DVD writers copy then certainly the secondary IDE bus will slow the process down as its interleaved writes, and you have 2 writers on it..