Fajr Sunnah time & prayer

Fajr is at 5.15am, but the azan is given at 5.35 and the Fard prayer is 5.50 Can I pray sunnah before the azan as the Fajr time has stared & then pray Fard with Jamaat. How can I tell the people that azan needs to be called at the time of dawn & not 15/20 min late & Fard is also after a very long gap after the dawn.