Total posts : 45366
That is definitely not Part 15 legal. No configuration with that antenna at 15 feet is going to get you a legal field strength. The average Part 15 FM will at most push 1,000 or so feet to a car radio, though typical compliant range is a few hundered feet. 1 mile is 5,500 feet a 1/2 mille is 2,750 feet. Dial back the coverage until it fitters out about 1/2 mile out consistantly on your best radio. At this point you appear to be at minimum 5x the allowed field strength.
(Edit: Do Note even a 1/2 mile of FM coverage is questionable from a legal standpoint, ballpark is 300-600 feet of coverage for compliant operation.)