As a loose rule,slugs work best from open chokes, but there's really no way to be sure w/o shooting some in that bbl. They won't hurt it.
Best results w/ slugs usually come with a dedicated bbl with either a rifled choke tube or full rifling (and good sights),but if you're hunting the thick stuff and can get close, it's not critical.
If you choose to use your present bbl and chokes, try the modified.