Extreme memory usage on profiles calendar

It seems that the calendar consume extreme amounts of memory on script execution. I'm currently moving my 120.000 userbase to 7.0.1 and when viewing the calendar section that shows you how many users have subscribed per day, I've been getting out of memory errors for /inc/classes/BxDolDb.php on line 255

I was forced to raise the php memory limit to 256 to get it to work, but the calendar needs some serious optimizations.