It depends entirely on how you play it. I only played through each level once - in each level I tried to complete a story mission for each target, reloaded my saves and retried things a lot (to be as sneaky as possible) and even completed the tutorial again (same one as in the first game) and it still only took me around 9 hours to finish it. Really glad I played it through family sharing instead of buying the Humble Monthly.
They’re quite pushy with “But there’s replay value!!!” now; when you finish any level they make sure to mention that there’s still a story mission you didn’t complete (usually there’s more than one possible one for the target) and to try that before you continue with the next level… I’m not the sort of gamer that likes replaying the same levels over and over again, though.