No you are not upper class if you are a married couple of teachers, that is exactly the point you made before about people overestimating their place in society. If you have to work to earn money you are not upper class, the upper classes already have so much wealth that they can live off the passive proceeds of that wealth.
Yes your dual income might but you in the top 15% of incomes, but wealth is the defining characteristic of the truly rich not income.