You have not mentioned the mane of medicines the child already taking. A detailed history of the fever (onset, type - continuous / intermittent etc, temperature, associated symptoms - like cough / cold/ vomiting / diarrhea
/ skin rash
etc). that would be helpful to understand the probable cause of fever.
However, please do not ignore a fever with 15 days duration. Get your child properly examined by a pediatrician
) - is used to decrease fever. It is a SOS medicine, means , it is to be given when temperature is high (>100 degree F). Dose is 10mg / kg (you have not mentioned your child's body weight).
)- is given to prevent gastritis
(damage of stomach due to acidity).
) - is an antibiotic drug, used to treat infection. Dose of oral suspension is 100mg / kg/ day in 3 divided doses for 5 to 7 days. However, the dose and duration varies on type and severity of the infection. As the cause of fever is not clear, I would not recommend the use of the medicine unless prescribed by doctor after examining the child. Don't give medicine yourself.
Please remember, improper use of antibiotic can create drug resistant infections - which are very difficult to treat.
Please get your child examined by a pediatrician and take medicines according to his / her prescription at doses specified.
Feel free to post if you have more queries.