Dose of paracetamol
is 10-15 mg/kg per dose 6-8 hourly.
Toxic dose of paracetamol is 10 times of normal dose.
Most of medication in children are based on weight if possible. As weight of children of same age may vary.So weight is better parameter than age.
As your child is about 15 kg a dose of 225 mg will be appropriate which is equal to 9 ml of calpol
So you need not to worry as you can give him 9-10 ml of paracetamol.