Does being overweight cause the pain from spondylolisthesis to be worse?

Hard to say: Being overweight makes any spinal problem more difficult to manage for the patient and difficult for the doctor to treat. Weight loss helps everything in the spine feel better and allows the doctors to treat it more effectively and safely.

Without question: The spine must support the weight of the body. Most people who who are over weight have the weight in their abdomen. They also then do stoop and not stand up properly. They tend to sit for long periods with poor back support. They have poor core strength with enormous stress on the low back with minimal help from the stomach muscles. This forces the lower back forward off of the pelvis.

Yes: Obesity plays a role in back pain in general and now you are adding an unstable level. It may also signify a lack of regular exercise as well which is a factor. Secondary to the obesity may be diabetes which can affect your nerves directly and lead to a neuropathy which may compound any stenosis symptoms if present with the spondylolisthesis level.