In the presented situation, are you obliged to stop before the major road?

Why?

The B-20 stop sign on the right requires you to come to a complete stop before entering the priority road. Simply slowing down is not enough, even if the road is clear. After stopping, you must give way to vehicles travelling on that road.

§ 21 ust. 1 rozporządzenia w sprawie znaków i sygnałów drogowych, B-20 „stop”