Sorry, but there's no way to get them back.
SODE jetways are an obvious improvement over the old buggy default jetways, and many of them were even the wrong size, so we had to adapt the scenery itself to the new, correct, ones. I couldn't imagine anybody wanting to go back to the old version.
Bad fps are not likely related to jetways, but to too high settings in two areas which are known for having bad fps even with a default scenery.