I can understand the organizers' desire for brevity. Assuming that even a fraction of the membership submitted a story, there would still be a considerable number of pages to be read. Though how they came up with the number 715, rather than say, 750 or 800 is quite beyond me.
In any case, 715 words is treading in the region of flash fiction more than short story. I've been a fan of flash fiction ever since reading Donald Barthelme's Forty Stories a few years ago; I've even tried writing some myself, although I've never quite managed to write one as short as 715 words. It's daunting, really, to try to convey a sense of character, setting, theme, whatever in so few words.
But I was listening to some music on my iTunes this evening, and I remembered that most song lyrics consist of far fewer than 715 words. Of course, musicians have the benefit of music to help evoke an emotional connection, but character and setting - plot even, if it applies - is all conveyed through lyrics. And we all have our favourite songs, those that resonate strongly with who we are and what we believe - so clearly a 715 word story is not only possible, it's almost more common than its longer cousins.
That helped give me a little more confidence. So I started writing a first draft - I finished that in 586 words. :)
