All the matters of Air Force are governed by Air Force Act, 1950 and the Air Force Rules, 1969. If you have been working for over 15 years, you would probably be a commissioned officer in Indian Air Force. There is a mandatory service for permanent commissioned officer and airmen to complete 20 years of service.
If you resign or take voluntary retirement from service now, you would not be able to claim complete pension and benefits provided to ex-servicemen. If you take voluntary retirement from service after completing 20 years of service, you will be eligible for the pension and benefits. However, if you had a short service commission officer, you are eligible to resign after 10 years of service as per the Rules and you have to serve for 14 years and you can resign now.
Otherwise, the Supreme Court has held that a person enrolled as a member of Indian Air Force does not have an unqualified right to depart from service at his or her will during the term of engagement. If you have any medical issues or any such problem, you can apply for premature retirement on medical or compassionate reasons by writing to competent authorities for the same. I would suggest you to stay for 5 more years if you are permanent commissioned officer or airman as it is a rather common practice in Air Force to seek premature retirement after completion of 20 years of service.
Reference: Air Force Act, 1950 and the Air Force Rules, 1969