nods And if we assume a citizen has at least some training for a +2 proficiency bonus and maybe a +1 or +2 in the ability score, that DC of 20 is yet more attainable -- hard, but possible.
D&D 5E adventuring parties can be set up with access to quite a few buffs (bardic inspiration, superiority dice, guidance, psionic energy dice, what-not... and in the case of stealth, the absolutely massive +10 from Pass Without Trace) and other ways to affect the dice (Lucky feat, divination dice, heroic inspiration, etc) to the point where 20 can seem easy to reach.