From GameWatcher: “The latest Two Point Hospital DLC is out now, and it’s set in the tropical climate of Pebberley Island. There are a lot of challenges to face, but do you need to have finished Two Point Hospital to play it? Do you need to have got to a certain point in the game at least to take on this new expansion?”
Source: N4G PC Two Point Hospital DLC – Do you need to finish the game to play Pebberley Island?