Gil,
If it's working okay, and it seems to be from what you've
said, then I probably wouldn't bother to change the way you're
feeding your antenna. There are probably several things that
you could do to improve your system, but 15 feet of coax isn't
going to make a lot of difference. But, the nice thing about
it is that you could make the change and see for your self if
there's any big differences (which will depend on the particular
frequency). As for the RF exposure, at 40 watts, it just won't
make any difference at all.
'Doc