Be sure to empty your cache and then test the speed of your page. Many people believe that the only way to make an image smaller is to scale the dimensions down some. With GIF images you have another option. A 4 bit gif is usually quite small. So bring the dimensions down a little and reduce the colors.
Interlaced images take longer to download than non-interlaced images.
Interlacing your background image does nothing more than irritate the surfer in most cases. Interlacing was implemented so we could get a feel for the graphic without having to download it completely. This allows us to navigate without having to wait for graphics to download all the way. Frankly, interlacing a background is a waste of time. We have to wait for it to download all the way, and frankly I don't care if I can figure it out sooner.