You probably won't notice much, even if it's working exactly as it's supposed to. VSL works best at preventing pouchitis, and you probably wouldn't notice that. If you already have pouchitis (and you haven't said anything that makes it sound that way) then VSL alone wouldn't be likely to fully clear it up. It also seems to help me keep pouchitis under control, but in my case it has to be combined with continuous antibiotics.
I'd still try it if I were in your shoes, at least if your insurance covers the DS (double strength) prescription-only form. One or two DS packets daily is usually sufficient. Some people don't tolerate it well, but I've been taking 4 packets daily for a long time.