A car weighing 1.5 tons is moving along a horizontal road. What is the weight of a car? Is it more or less gravity?

In the case of movement on a horizontal road, the weight of the car will be equal to the reaction force of the support, which in turn in this example is equal to the force of gravity:
P = N = F = mg = 1500kg * 10m / s2 = 15kJ
If the car moves along an incline, then its support reaction, like the weight, will decrease, this can be seen if you paint the movement along the axes and arrange all the forces.