If you are going to give combo sick/vacation PTO days, I think the minimum number that is reasonable is at least 4 weeks. That way, people can have 2 weeks of sick time, and 2 weeks of vacation.
But there is also half-hearted pressure from HR to consume more than about 30% of our total PTO, combined with unstated pressure from management in general to consume less than 50% of it. Everyone ends up worrying about the exact number of socially-acceptable days to take off per year rather than just living their lives. I've gotten used to it but when I hear about European standards, I'm just green with envy.