use constant NUM_ELEMENTS => 15;
# Get the starting_array from somewhere
my @starting_array = populate_somehow_with_data();

my $start_index = 0;
while ($start_index <= $#starting_array)
{
    my $end_index = $start_index + NUM_ELEMENTS - 1;
    $end_index = $#starting_array if $end_index > $#starting_array;

    my @array_slice = @starting_array[$start_index .. $end_index;
    $start_index += NUM_ELEMENTS;

    # use @array_slice here to do what you need to do.
}