I'd like to share how I solved this problem. IOS 250 did not work for me, or at least the one I have (which I know is outdated). I'm paranoid about installing new things, so didn't want to replace the one I had. I ran SysCheck and noticed I did not have any IOS 224 installed, which some said worked for JD 2015.
Based on other's advice here in another thread, I ran ModMii on my PC and had it evaluate my SysCheck log. It recommended a whole bunch of updates, including adding cIOS224[57]-v5.1R so this is what I did, added 224 but nothing else since I hate updating my Wii.
Now JD 2015 works!
If you don't want to run ModMii, I've uploaded the IOS 224 update that ModMii downloaded for me. Just change the settings for JD 2015 so it runs using IOS 224, it worked on both USB Loader and Configurable USB Loader.
http://s000.tinyupload.com/index.php?file_id=69963856606550188678