^^^Ignore the comment above.
Back to the two boats in question... I've been in both and put them to the test. It's a tough choice and really depends on what your goal is. The rear lockers on the x-15 are tiny and makes it really hard to put extra weight in for surfing. However the rest of the storage is great. Both boats have plenty of room for under seat ballast surfing bags, the rear lockers on the vlx are alot bigger though. I like the height of the tower on the x-15 much better, illusion is to short. New illusion xs tower is taller though. Of course the x-15 comes with a better stock stereo.
As far as wakeboard wake goes to me they were almost the same, a little bigger in stock form on the vlx but both very nicely shaped. I did not add any extra weight. Neither boat is really that problematic with weight placement in my experience which is good. Put about 1200 pounds of extra ballast ontop of the stock 900 in the x-15 to get the the surf wave size as the vlx with just 750 in the rear locker and 3/4 mls full.
I really don't think you can go wrong with either boat, I like them both alot.