Conditional custom field query

I found this: http://codex.wordpress.org/Displaying_Posts_Using_a_Custom_Select_Query
I have modified the date to retrieve the last 15 days. It’s untested, but should work.

$expireDays="15";

$querystr = "
    SELECT $wpdb->posts.* 
    FROM $wpdb->posts, $wpdb->postmeta
    WHERE $wpdb->posts.ID = $wpdb->postmeta.post_id 
    AND $wpdb->posts.post_status="publish" 
    AND $wpdb->posts.post_type="post"
    AND $wpdb->posts.post_date >= ( CURDATE() - INTERVAL $expireDays DAY )
    ORDER BY $wpdb->posts.post_date DESC
 ";

$pageposts = $wpdb->get_results($querystr, OBJECT);