To have SVG images with the weight of a few kb you should completely create this image with Illustrator, but it's a very complicated thing, or use an image already in svg downloaded from the sites.

When I started to "play" with the file speedcam.zip I also tried Inkscape, but the quality is very bad and I think it do not save the svg files in the correct way for iGO.
The first real tests I did with Illustrator CC 2015, but the files were blocking the navigator, oddly it does not save the files in the correct way for iGO but I lost a month to understand it.
I switched to Illustrator CS6 and I was able to convert the normal images bmp, png, jpg to SVG, but more than the starting images are detailed and with many nuances, and the more the file becomes "heavy".
By default, Illustrator saves files with the decimal factor 3, (the greater the number, the higher the quality, and vice versa), you can try to save with 2 or with 1, but you have to see the icons maintain a satisfying quality.
Some of my speedcam.zip files are also 10 Mb, but luckily they work without problems .......