I've got a 1979 300d with most likely original rear suspension components

Last weekend I loaded 3 water bottles (approx 165lbs) in the trunk

We I got home I noticed the rear was squatted pretty good.

Is this normal?

Maybe I need new springs?

I'm guessing two passengers in the rear seat would be 250-300
so what's up?

Surely a 4 passenger car should be able to carry 4 adults and luggage.