Is it mandatory in the presented situation to stop before entering the intersection?

Why?

A green left arrow is displayed by the S-3 directional signal above your lane. It permits a left turn and does not itself require you to stop if you can continue safely. A mandatory stop before turning applies instead to an S-2 conditional arrow displayed beside a red light.

§ 97 ust. 1 i 2, § 95 ust. 1 pkt 1 oraz § 96 ust. 3 rozporządzenia w sprawie znaków i sygnałów drogowych