The following is a sampling of websites available about the 15th Air Force:
- The Fifteenth Air Force: http://www.15thaf.org/
- 15th Air Force, United States Army, 1943-1945: http://www.2ndbombgroup.org/15thAirForce.htm
- 15th Air Force Headquarters, Bari, Italy, in WWII: http://www.frankambrose.com/pages/15th.html
A book published in 2014 on the 15th Air Force, may be of interest. It is Forgotten Fifteenth: The Daring Airmen Who Crippled Hitler’s War Machine by Barrett Tillman, Washington, D.C.: Regnery History Publishing, 2014. A review in the 8th AF News said: “The U.S. Fifteenth Air Force fought in southeastern Europe, in many ways the backwater of the European Theatre. While the Eighth Air Force hit Germany, the Fifteenth took the battle to the factories and oil refineries out of range of England-based bombers. These targets were vital to the Axis war effort, and the Germans knew it, covering them with a thick layer of defenses including both fighters and antiaircraft guns. The pilots and aircrews of the Fifteenth fought through these defenses to hit the Nazi war machine where it could least afford it.” To see what the author has to say, click here.
WWII Netherlands Escape Lines 
I am a professional researcher at the National Archives, College Park, Md.I am writing a book on the Tuskegee Airmen, 99th, 100, 301st and 302nd Fighter Squadrons, 332nd Fighter Group, 15th Air force. I am researching various shoot downs of pilots from these units. The first is Lt. Robert L. Martin, 100th Fighter Squadron, who was shot down in Yugoslavia, on 3 March 1945 in the Zagreb area, He was helped by unnamed partisans and a Major Udelitz who was the principal liason between the British Mission and the Partisan Headquarters. Anything you have on this pilot and the incident. He travelled with partisan help from the Zagreb area to Kravarakr to Topusko, to Rakovica, to Zara and ultimately to Bari.
Any help you could give me would be appreciated. I may be able to help you with records here at the National Archives, USA.
Michael
Michael, are you still researching this topic?
Bear