Yes 20 PSI is about half of what is considered the bare minimum. Is it even producing water at that pressure? The other questions is, whats wrong with the house's bladder tank? A well water home w/bladder tank will run around 36-40 psi. City water is around 50-60 psi.
RO systems without a booster pump blow. Even with good city tap water, a booster pump will really make it a good investment.
Ive run 2 systems without a booster, and one with. I cant believe i never had a booster before now.