Get traffic. The more traffic, the lower your Alexa rank. Not that it matters much, as already pointed out by others. BTW, your page rank has nothing to do with neither traffic nor Alexa rank. You probably inherited it from the domain name. P.D. An Alexa rank of 15 MILLION? I've never seen something THAT low!
Here's how to improve your Alexa Ranking almost overnight .... and here's why Alexa ranking is pointless.