If it's a straight burn of data, or a prepared Video_TS or image, then something's horribly wrong.
That's more than 6 times slower than a 1X burn of data, if I recall.
You could check your hardware & driver situation with Nero Tools. Could be the ASPI layer (if I recall there are other things than ASPI for external drives). Could be the controller driver. Who knows what.
CdFreaks forum is the place to go for techical answers. (Use their broken search function before posting).