Can you say why you need to save this image as SVG?
As it is a near-photographic image, it is not really suitable to save as vector. Illustrator's native format may work just fine (for such an image, I imagine it's barely smaller though), but SVG is way more verbose. Imagine you have an actual high-resolution photo and want to save that as an SVG; at that point, each individual pixel would need saving as a very tiny colored square with four coordinates.
Did you check if there is nothing out of the ordinary in the SVG Options dialog? Also, would it be alright to save it as a compressed SVG as well?
The only other option (unless you must save it as a vector image) is saving it as a JPEG (or any other bitmap format, for that matter), which ought to do wonders here.