While looking for posts in the series, this plugin makes two database queries for each post in the series : one to find out if the post is published, and another to get the part number in the series. So if you have 30 posts in the series, you will get 60 queries from this plugin alone on each post belonging to that series. I found this very wasteful, and rewrote one function so that it only uses one database query, no matter what the number of posts in the series. I think the author should be interested…
Basically, in the file series-utility.php, replace the function
function get_series_order($posts, $postid = 0, $skip = TRUE)
by the following one :