SVG export in comparison to PDF?

I am using GenomeDiagram from BioPython, which is based on ReportLab to
generate pictures, to draw some graphs/maps on the genome. The data is in
general huge, so that export of a picture out into PDF file takes a few
minutes. But the problem is with export in SVG files: I waited over 40
minutes and it still hasn't finished writing to disk (BTW, the process was
using >1Gb of RAM, but only 1-2% of CPU - looks strange to me, is it?).
Is it an issue in ReportLab or a pure format structure issue?

Best,
Ilya