Tile Based Game - Slow to Load

Hi Every1.

The tile based game that i am doing is currently loading 25 x 25 pixel pngs to create the map. The problem i am having with this is that it is taking too long, i.e. circa 30 secs at least. I am loading the tiles via this way:

private function  loadBitmaps():void 
            if (_currentId >= _mapArray.length) {
                    if (_loader.content != null) _loader.unload();
                    _loader.load(new URLRequest(_mapArray[_currentId].img));

private function completeTile(e:Event) {
            _mapArray[_currentId].bmp = (_loader.content as Bitmap);

the initial loadBitmap is called once the user chooses the map.
My question is, how can I improve the load speed? Im sure there is a more efficient way to load tiles that correspond to an array.

Thanks for your help.