Burnwinter I mean, 15 goals would be 12 more than our second choice striker got in the league last season (crude comparison, I know...bear with me).
And yes, I want an upgrade on Havertz at CF but simply having another viable option at CF will make a pretty big difference to how we fare in the short term. It'll ensure we don't knacker Kai and afford him more flexibility in the role he plays in our squad, which in itself is a bit of a multiplier (eg. we could play with two strikers in some games or drop Havertz into midfield). In a situation where we've started Havertz and it's not working, having someone on the bench who provides another option (one with skills Havertz doesn't have)...well, we didn't have that last season for the most part. Buying Sesko gives us more options in the short-term (which should significantly improve the output of the team) and has the potential to be a monster in the longer term.
My point is, I think there's substantial scope for him to improve the outlay of our team without hitting 20 plus. If Sesko never achieved those kind of numbers for us, I'd be disappointed but I do think this signing isn't just about his individual contribution, it's also about what he adds to the team.
Glass half full take for ya.