At first, please check the DMA settings of your drives. Easiest way should be Nero Info Tool.
Then: Please describe the way, you were burning your disc. Are you writing the data straight away from your HDD to disc or is there some conversion (like AVI to DVD video) involved? I ask this, as the lowest speed of recent LG drives is 4x. If there were a media issue, then plain burn time would be approx. 15 minutes.