You are right, it takes almost 15 minute which is too much

below is complete code.

#! /usr/bin/perl
use strict;
use Math::BigFloat;
Math::BigFloat->precision(0);

sub GetINDirFiles {
        my ($path) = @_;

        opendir DIR, $path or die $!;
        my @files = readdir DIR;
        my @files = grep {!/\_ACK_/} readdir DIR;
        closedir DIR;

        return(@files);
}

sub GetOUTDirFiles {
        my ($path) = @_;

        opendir DIR, $path or die $!;
        my @files = readdir DIR;
        my @files = grep {/\_ACK.xml$/} readdir DIR;
        closedir DIR;

        return(@files);
}

# Main
my $inpath = "/AAA/BBB/CCC/IN";
my $outpath = "/AAA/BBB/CCC/OUT";
my $outsuffix = "_ACK.xml";
my $insuffix = ".xml";                #    Added by me 
my $timethreshold = 900;       # set time threshold in seconds (900 se
+conds equal 15 minutes)
my @delindex;

my @infiles = &GetINDirFiles($inpath);
my @outfiles = &GetOUTDirFiles($outpath);

my $index = 0; # index used to get string position in array
foreach my $infile (@infiles) {
        $infile =~ s/(.*)$insuffix/$1/g;      # remove suffix to do co
+mparation # Added by me
        foreach my $outfile (@outfiles) {
               $outfile =~ s/(.*)$outsuffix/$1/g;    # remove suffix t
+o do comparation
               
               if ($outfile eq $infile){
                       push (@delindex, $index);      # get list of st
+rings to be removed from array
               }              

        }
        $index += 1;
}

delete @infiles[@delindex];    # remove strings 

my $currenttime = time;        # get current time from system (epoch t
+ime)
foreach my $file (@infiles) {
        next unless (-f "$inpath/$file$insuffix");    # ignore directo
+ries   # INSERT SUFFIX AGAIN ($insuffix)
        my $mtime = (stat "$inpath/$file$insuffix" )[9];      # get mt
+ime from file (epoch time)   # INSERT SUFFIX AGAIN ($insuffix)     
        my $diff = ($currenttime - $mtime);

        if ($diff > $timethreshold) {  
               print "\n - file " . $file . $insuffix . " in " . $inpa
+th . " directory was created at more than "  . Math::BigFloat->new($d
+iff / 60) . " minutes.";    # INSERT SUFFIX AGAIN ($insuffix)
               
               # PUT THE ACTION THAT YOU WANT DO HERE!!!

        } 
}
[download]

i need to do it on regular interval like 5 minute or 15 minute, using an tool i use. so it really does not make sense if i check the files which i have already checked and i would not mind if this completes in minute or less then this but 15 minute is really too much

kindly assist

-KAKA-

Your code can be optimized a lot. Here is some proposal but I cannot test it as I do not have your directories at hand. I added comments to explain what I am doing so I hope it helps:

my @infiles = &GetINDirFiles($inpath);  
# instead of having an array with the outfiles use a hash for faster l
+ookup
# also remove suffix at this stage already, no need to do it again and
+ again in the loop
# you need to escape your suffix variable in \Q...\E for special chara
+cters such as the dot
# only remove the suffix at the end, no need for (.*)
my %outfiles = map { s/\Q$outsuffix\E$//; $_ => 1 } &GetOUTDirFiles($o
+utpath);

my $index = 0; # index used to get string position in array
foreach my $infile (@infiles) {
        # see above re the replacement
        $infile =~ s/\Q$insuffix\E$//;      # remove suffix to do comp
+aration # Added by me
        # instead of loop through array of outfiles do hash lookup
        push (@delindex, $index) if exists $outfiles{$infile};
        $index += 1;
}
[download]

UPDATE: Forget my code above. You can write this as:

my %outfiles = map { /(.*)\Q$outsuffix\E$/; $1 => 1 } &GetOUTDirFiles(
+$outpath);
my @infiles = grep { /(.*)\Q$insuffix\E$/; not exists $outfiles{$1} } 
+&GetINDirFiles($inpath);  
print "@infiles\n";
[download]

and it should be fast.

UPDATE 2: Here is the full story.

use strict;
use warnings;

sub GetINDirFiles {
        my ($path) = @_;
        opendir my $dir, $path or die $!;
        return grep {!/\_ACK_/} readdir $dir;
}

sub GetOUTDirFiles {
        my ($path) = @_;
        opendir my $dir, $path or die $!;
        return grep {/\_ACK.xml$/} readdir $dir;
}

# Main
my $inpath = "./IN";      
my $outpath = "./OUT";
my $outsuffix = "_ACK.xml";
my $insuffix = ".xml";     
my $timethreshold = 900;       # set time threshold in seconds (900 se
+conds equal 15 minutes)

my %outfiles = map { /(.*)\Q$outsuffix\E$/; $1 => 1 } &GetOUTDirFiles(
+$outpath);
my @infiles = grep { /(.*)\Q$insuffix\E$/; $1 and not exists $outfiles
+{$1} } &GetINDirFiles($inpath);  

my $currenttime = time;        # get current time from system (epoch t
+ime)
@infiles = grep { -f "$inpath/$_" and ( $currenttime - (stat "$inpath/
+$_" )[9] ) > $timethreshold } @infiles;

# now you have all input files w/o corresponding output file that are 
+older than 15 minutes
for (@infiles) {
        print "File $_ in $inpath directory was created ". ( $currentt
+ime - (stat "$inpath/$_" )[9] )/60.0 ."minutes ago.\n";
        # put your action here
}
[download]

Do you want to compare the names of files or the contents of files? Could you give an example of what data you're trying to compare, and what output you expect to get?

    my @files = readdir DIR;
[download]

Sorry. but that is commented, i dont know where the # gone

.  # my @files = readdir DIR;

-KAKA-