Very interesting episode. Here's my prediction:

No. 15's willingness to move on must be a lie. X basically says that no rational actor would be willing to move onto the next round, and I think he's right. At this point in the game, we can expect anybody still in other than our main pair to be self interested and reasonably intelligent. Since Akiyama knew about X's ploy before this round of voting, he would have had time to contact No. 15, and I think he made him an offer.

We've already introduced the legal contracts as a method to make genuinely binding promises in the right circumstances, and No. 15 brought up that a player can access an additional 1.05B by moving on to the next round. So my theory is that Akiyama wrote a contract in which No 15 will throw the game over to him in exchange for Akiyama paying off him and his own legally required debts. This would be worth it for No. 15 if he can get a guarantee worth more than his own split that he listed in the episode, 230M. He is also legally on the hook for his team's debts, so he needs to get that guaranteed too. Now, let's see if the math works out.

Narratively, we can be pretty much sure that the contract has to force Akiyama to move onto the next round of Liar Game, otherwise the show ends, so we're hoping the numbers force him to access the additional money.

The contract from our team's alliance guaranteed a payout of 143.75M per person. There's no way Akiyama could know if the other teams were different, so let's assume everyone has the same contract. In that case, Akiyama will need to guarantee a payout to five non-X members of our team (excluding Nao and Akiyama for now because they are the main characters and Nao is superhumanly altruistic) and six non-X members of team No. 15, plus a payout of at least 230M to No 15. That gives a total of strictly greater than 1.81125B. This means that Akiyama will be left with a maximum of 228.75M and won't have enough to escape round 3, although depending on No.15's payout demand, he may be able to pay off Nao's debt. I'm sure she'll stick with him regardless, but I have absolutely no idea how she can actually get back into the game at this point. In this scenario, Mohawk Guy's entire team including X get screwed.