Only one match needed.

if (length($string) > 15) {
  $string =~ s/^(.{0,12})\b\s.*/$1.../gi;
}
[download]

cLive ;-)

Update:

MeowChow pointed out typo - missed out .* (had it on other machine running demo :)

Actually, if there's a chance that the first word will be longer than 15 chars, you'd need to expand this a bit to cut off the end of the first word. Oh hell, let's change a few things here:

if (length($string) > 15) {
  unless ($string =~ s/^(.{0,12})\b\s.*/$1.../gi) {
    $string = substr ($string, 0, 12) . '...';
  }
}
[download]

Finally, I disagree with MeowChow (below). I think \b *is* needed. Otherwise this could happen:

A Satsuma - Orange would become A Satsuma -... </CODE>