Flap 2, 180 knots selected will create a good sink rate. If you take speed brakes too it'll drop like a stone - SO BE CAREFUL < 4000'!
The secret is to act early. FMGC predictions are all well and good - provided the flight plan is sequenced, descent winds are inserted etc...... but always back it up with the basics i.e. 3 x your height + 5 miles to slow down (10 in the early days!) So at 15,000' you need (approx) 50-55 track miles.
If you can see you're already going slightly high on profile - act on it - early. Also look at the wind arrow on your ND headwind or tailwind - act accordingly. as others have said if ATC ask for something you can't comfortably achieve tell them.
Practice makes perfect - good luck.
A4