If you are trying to burn a movie-sized file (not actually a movie, just for anyone's reference) then that's actually not a bad time in reality. It can, of course, depend on the software you're using to burn it.
if you're burning data then that's bad. could be a failing unit, or the unit needs a firmware upgrade to recognize the disk, or you got a bad batch of disks.
if you're converting a video to a dvd movie then it's about right for programs that aren't optimized for multi-core processing