Inkscape is notoriously verbose in the SVG it produces.
It looks like the file you started from was part of the
Etiquette icons set, which is probably why it had a lot
of extra information.
The comix SVG file contained a whole lot of unused
I was able to cut the file size from 19kb to 5kb simply
by deleting the unused defines. Obviously the file
size could be shrunk even further with manual tweaking
of the markup or using compressed SVGZ but I'm not
going to do either of those.
(By the way it would be great if you could enable SVG
support in Comix. Gdkpixbuf optionally supports SVG
with the help of librsvg, so maybe if there was some
way to fallback to gdkpixbuf you might be able to get
SVG at no extra cost.)