With your changes i'm at the following code and have a real life application improvement from 0.055 seconds for a whole "syncToDF" loop down to 0.049, which is already pretty respectable. Additionally you've helped show me where i need to keep my eyes open. Thanks a lot! :D

    my ($tile_index,$rx,$ry,$y,$x,$xScaled);
    
    my $bxScaled = $bx * 16;
    my $byScaled = $by * 16;
    
    for $x ( 0..15 ) {

        $rx = $bxScaled+$x;
        $xScaled = 16 * $x;

        for $y ( 0..15 ) {
            
            $tile_index = $y+$xScaled;
            $ry = $byScaled+$y;
            
            if ( 
                !defined $tiles[$rx][$ry][$bz][type] || 
                $tiles[$rx][$ry][$bz][type] != $type_data[$tile_index]
            ) {
                $changed = 1;
                $tiles[$rx][$ry][$bz][type] = $type_data[$tile_index];
            }
        }
    }
[download]

Now to see whether there's some more good hints. :)