SKT has a massive amount of content, in most of the feature-categories that Roll20 offers (characters, handouts, pages, rollable tables, and so on). Even with the Transmogrify tool of Roll20 it would be a lot of work to move everything from SKT into another pre-existing campaign. I agree with Scott's suggestion. It's likely easier to move the important bits from your existing campaign (Character journals in particular, using the Character Vault method or Transmogrify), into an SKT installed game.