I did this a few years ago when I first got a 13x13 and lots of people put guesses down. Now I am doing the same with the 15x15. So far I am quite surprised as people seem more confident in my solving ability, many people are guessing times that I think are closer to what I actually expect to get, whereas with the 13x13 I was much faster than most people expected. This time the puzzle is magnetic and fully cubic so I do expect the solve to be a lot faster than it would be on other 15x15s. I held off getting a 15x15 until DianSheng released a magnetic one and I will probably hold off getting other cubes larger than 13x13 until there are magnetic ones available. YuXin have released a 14x14 and are soon releasing a 16x16, both these puzzles are fully cubic which is somewhat exciting but they are not magnetic so I am not getting them for myself, if anyone wants one then I can order one in for you though.