A very easy way of doing this involve the use of the core modules Tie::File and List::Util:

use strict;
use warnings;

use Tie::File;
use List::Util qw/first/;

tie my @lines, 'Tie::File', shift @ARGV or die $!;
my $line15chr = first {/^.{15}$/} @lines;
print $line15chr,"\n" if defined $line15chr;
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Hope this helps

citromatik