No, the 15% is just Krankenversicherung (health insurance). There's also Pflegeversicherung (nursing care insurance), Arbeitslosenversicherung (unemployment insurance) and Rentenversicherung (national pension fund).

When I take an average salary (3000 euro monthly gross salary) and put it into a tax calculator, the net salary comes back as about 1950 euro, so the different between gross and net salaries is about 35% in that tax bracket.