The specs on the software and OS as Tom suggests would be helpful. But since you keep your system alive and get further along, why not try disabling your screen saver and setting your system preferences to NEVER turn off the hard drive, as well as ensuring App Nap is off as suggested by timfo. See if you get through a complete export.
DVD's seem to take a long time. It's slow to write to them and it's also slow to compress the media to the format. If I'm correct, the RAM in your system isn't really doing much for sharing, it's mostly for loading clips and playback. When exporting it's going to rely heavily on the GPU and then some on the CPU, so if your GPU is less than 1GB of VRAM then it's gonna be slow.
What resolution are you exporting to? Master file? or something compressed?