Just to give you a point of reference:
At my KMSY feed I am approx. 6 miles from KMSY. The antenna is a KB9VBR J-pole mounted on a 30' push-up pole. Coax is about 70' of LMR-240 cable (mini-RG/8). NO PREAMP. Receiver is an old radio Shack PRO-2006.
Ground is flat- Louisiana flat. I probably have line-of-site with the ATC antennas.
I am able to receive 98% of the ground vehicles and planes on the ground, plus 100% of ATC and planes airborne.
With your location 15 miles from the airport, I would concentrate on raising my antenna to maybe 50' in order to get the
most height. Height is going to be your most important element in receiving anything on the ground. All the amplification in
the world won't help if you don't have a signal to amplify. If there are any tall buildings or hills between you and the airport, that will reduce the signals even further.
My suggestion is to work it in stages.
First get a good antenna (yagi, if possible), ground-plane or J-pole if yagi is not available. Put it up as high as possible and put some good coax on it.
Second, see what you can and cannot hear and if the ground signals are scratchy, but you can hear them, then try the preamp. (20 db)