How is calculated the descent rate? in my case with A320 pilot2atc give me the values of 1500 FPM rate  , then i start my descent on the green arrow fixing -1500  in plane but they arrive to the next waypoint altitude very soon.

what is wrong?

thanks

P2A does not calculate the descent rate.  You have to enter it.

For an airliner, 1800 FPM is a good starting point.

When flying, to make the Descent go according to plan, you need to fly the planned GS as well as maintain the planned descent rate.  Also, don't forget to slow down to 250kts below 10000 ft.