I don't know much statistics, but it seemed like the average of the last x samples would do what you want. This code behaves how I interpreted what you want, changing samples will change how much data it holds to average over, that would be a matter of preference on your part. I would think if you don't restrict the samples you'll just end up with jibberhish, assuming you are sampling some source for this data on a regular basis. If that is the case than this will tell you if at any point the last x samples averaged over 15:1.

use strict;
use warnings;

use Data::Dumper;

my @que    = ();
my $sample =  5;

sub average_ratio {
    my @data = @_;
    my $ratio = 0;
    
    for (@data) {
       
       $ratio =  $ratio + ($_->[1] != 0 ? ($_->[0] / $_->[1]) : 0);
    }
    return $ratio /  scalar @data;
}
    

while(my $line = <DATA>) {
  chomp $line;
  my ($po, $fr) = split (m/\s/, $line);
  push @que, [$po, $fr];
  shift @que if @que > $sample;
  my $avg = average_ratio(@que);
  print "Adding [$po,\t $fr]\t makes the avg_ratio: $avg\n";
  print "DANGER\n" if $avg > 15;
}


__DATA__
0 0
0 0
150 10
0 0
200 40
210 40
220 40
220 30
0 0
0 0
0 0
220 20
220 10
220 05
220 01
220 100
220 100
2200 100
2200 2
2200 2
0 0
2200 1
0 0
0 0
0 0
0 0
0 0
0 0
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