I seem to remember in my early training a conatant humming in my right ear " Ball ..... ball in the middle .... watch that ball now ..." and I am no different with my students. Once your in the habit of checking it, it's not a big deal to keep it there. In a C150/152 the pressure required should not be that great. I've never flown a C172/PA28 type plane though that didn't have a rudder trim, although it's amazing how many people haven't been taught how to use them, and the number of PA28 ones that have just been wound off the end of the spindle.