Go to \Data\Scripts\Intro and delete the files there. Should give you a blank background then (or trash your install). Don't forget to backup before trying.
How about choosing the one, which don't eat up lots of resources, copying it several times, and rename them?
Like, there is an "intro_waterplanet.thn" file, which is only 8 kilobits.
And then, there is a "gasminer3.thn" which is 46, and in my opinion, it can cause you more lag than the waterplanet one.
So, copy the waterplanet.thn, and rename it gasminer3.thn, and also delete the original gasminer file.
Theoretically, it will try to load the gasminer one, but instead it will load the waterplanet one.
Hope this one helps, I'm going to try this one if I arrive at home.