In this situation, is it permissible to drive through the intersection without reducing the vehicle speed?

In the video you are approaching a junction with traffic lights in town; the traffic lights show green, and the roadway ahead of you and the pedestrian crossing are clear. You are allowed to drive through the junction without reducing the speed of the vehicle. The answer is: yes.

The Regulation on road signs and signals states that a green signal means permission to drive beyond the traffic lights, and the Road Traffic Act requires particular caution when approaching a junction. However, no rule requires you to reduce speed before every junction - if you have green, nothing blocks the roadway, no pedestrians are finishing crossing and there is space beyond the junction, you drive through at your current speed, within the limit in force on this street. You must slow down when the situation requires it: a pedestrian on the crossing, a vehicle turning from the opposite direction, a traffic jam beyond the junction, a tram finishing its passage. Particular caution here means observation: you watch the crossings on both sides and the intersecting roads entering the junction, because not everyone stops on red, and the traffic lights, which after a long green may soon change to amber. Driving with your foot ready to brake, but without unnecessary slowing down, is correct in this situation.

Legal basis: § 95 para. 1 point 1 and para. 2 of the Regulation on road signs and signals; Art. 25 para. 1 and Art. 19 para. 1 of the Road Traffic Act (Prawo o ruchu drogowym)