15% Rule is simply only pertaining to a trade after the contest starts, Meaning if a stock has a painter. Lets say for example stock is really illiquid.
And has and bid of $1.00 and a ask of 2.00. It Doesn't let anybody take advantage of say selling 100 shares near the close at $1.00 on say the 31rst of january (You use your trade to buy in $1.00 in the contest, and then buy a 100 shares close to the first day of febuary at the end of the day at $2.00 and selling it then in the contest at $2.00 with a total of 200 shares traded between the two days. And say you have 100% gain on no news, as we know we really couldn't do that in real life so that shouldn't be allowed in the contest. It basically is there to stop painting (deciding a contest on illiquid stocks), but with $7,500 dollar volume, I doubt the 15% rule will ever even come into play to be honest. Hope this helps.
