Flash has a test function for a reason...
Why do you need to upload a preloader to Newgrounds just to test it? In case you didn't realise, Flash does have a test function. So use it!
And anyway, 7.4mb for a preloader is completely and utterly pointless, that means you've only got 2.6mb for your movies/games. Seriously, preloaders are meant to be simple, so stick to the Newgrounds preloader or make something with a much smaller file size, my preloader is just a bar that fills up and it's probably about 50kb max, and they're just fine.