DVD-A is a lot slower in the render mode, use Vegas to render, put two hours on the time line, then add any chapters, then render as MPG2 and AC3 this helps keep the file size down. Use a avg rate of 4M p/s for the conversion, or do 10 Min's of render see what size you get then multiply it and see if it fits in to a DVD, you should aim for about 4.3Gb for the DVD as DVD-A seems to thinks the files are bigger for some reason

DVD Shrink is used to strip menus & bonus features and the likes you end with the original footage is of no practical use here, even if use for re-render as it will degrade the quality.

I have managed to get 2hours .40mins on a recent project using 2 pass, its OK but not brilliant.

If no fancy menus are required, may be easier to copy into a DVD -Recorder and saving the hassle of encoding and burning.