It will take the same amount of time to download whereever or however a user downloads it. When the page has been seen once it will be in the users cache (at least until they clear it)- more than that you cannot do. If it was on a later page you could have it download in advance at a page that was less 'big'.This is a vast image and you are going to have to play with it a bit to get it to load faster. It is currently a whopping 398930 bytes. 
I ran it through the jpeg optimiser available here: www.xat.com (download it: It is a snip to use) and that immediatly reduced it to 87170, still way too big but a fifth the original. I will email you that version for what it is worth.
You have several choices. You could try splitting the image up into smaller chunks and optimising each, or comprimise on the look you are after and use smaller images.
Certainly you need to do something, it is far to large as it is.
------------------
Katherine
www.inkkdesign.com
-*-*-*-*-*-*-*-*-*-*
"Dogs have owners, cats have staff!"