Four Zeus symbols grant players access to the most exciting part of the game. Regardless of whether 4 or more symbols appear, the number of free spins is always 15. However, a larger number of scatter symbols is still desirable, as they provide instant payouts of x3, x5, and x100 for 4, 5, and 6 Zeus symbols, respectively.
Free spins are similar to the base game, but a key element appears - the Global Multiplier. It continues to grow throughout the bonus round. Each multiplier applied to a win is added to the total sum. And to make the game even more interesting, after applying a new multiplier to a win, the global multiplier is also applied to it.
It would be great if all new multipliers contributed to the total sum. But instead, they are only added when there is a win. Therefore, you will often see multiplier symbols simply wasted.
If you check the Gates of Olympus paytable, it states that special reels are used during free spins. This doesn't mean the layout changes, but the frequency of valuable symbols has likely been increased to ensure greater winning potential in this round.