Could you tell me what is the success rate for surgery for spondylolisthesis?

Great indication: Spondylolisthesis is generally considered a great indication for surgery (especially if there is excess motion at that segment on flexion vs extension xrays or if accompanied by leg symptoms) and most (>85%) are considered "successful" (50% improvement is common definition in studies). With that said, surgery is not "needed" unless there is instability or neurological deficits.