Which power cable is suitable for parking lot lights and socket?

Depending on the length. If low wattage, then 1.5 is sufficient.

Up to 70m!

The total load should not exceed 1000 watts in length if it is to remain at 1.5.

we have laid 5x2.5mm2 of the same length, black underground cable

1000 watts is not that much. If you connect a kettle to it, that is already too little. Therefore 2.5.

The cross-section of the cable is designed according to the fuse rating. So normally 16A. Accordingly, the cross-section at 70m should be 6 square millimeters, and even if it is only fused with 6A, 2.5 square millimeters are needed for the same length.