Its not quite as bad as it seems
Max take off weight of a 152 is 1670 lbs
from that subtract a 14 stone (ie fattish male) instructor and a 14 stone student and full tanks (20 imp gallons @ 7.2 = 144) and you are left with 1134 lbs for the basic weight of the aeroplane.
Cessna quote 1133 lbs for the standard empty weight of an aerobat. In reality most are a bit heavier depending on avionics, but most instructors and students are a bit lighter, especially instructors because they can't afford to eat.
I'm lucky in that most of my instructing has been on PA28, but I did the initial and aerobatic instructor course on a 150. I seem to remember that as you, the student, the fuel and the CofG all coincide it is difficult to get it out of balance unless you crawl in the back (some 150s could actually be approved for a third child seat with very skinny parents).
If all else fails thermalling can double the rate of climb !