If your 15-month-old child has a fever and a runny nose, it is recommended to treat the fever with acetaminophen. The dosage should be 10 to 15mg of medication per kg of your child's weight, every 4 to 6 hours, up to a maximum of 5 times per day. It is also important to maintain good nasal hygiene by using saline water solutions. If the fever persists for 72 hours or more, if your child is having difficulty eating or drinking, or if other symptoms develop, it is advisable to consult a healthcare professional.