I downloaded that file, opened it in Inkscape, selected all of the objects, and ran the extension. It took about a minute, but appears to have worked– it said that it reduced the amount of air-plotting time by 97%.
If the total number of objects is too many, you might try selecting only part of them (Half? One quarter?) and optimize that many at a time. The longer path between the optimized parts will have a negligible impact on the overall plotting time.
