If you have the Lat/Lon of two points, you can get delta Lat and delta Lon and convert this to a distance along latitude and a distance along longitude, and use Pythagorean theorem.
Have you looked at pages like http://www.movable-type.co.uk/scripts/latlong.html? This has several ways of computing distance. So as you go through your list of points, you use the formula to calculate the distance from each point to the point of interest and keep only those that satisfy R<15 miles.
