If you are lucky enough to handle Xyz Monsters such as "Numbers", including #25 and #39, then the 15th floor will become bit of a challenge. Just follow these:
Wave 1 - Easy
Guardian Baou is the first. If you have LIGHT monsters, then the damage is 3x.
Wave 2 - Challenging
Skull Knight is next but ATK is 2650. "Number 25: Force Focus" must be included in your Extra Deck for preparation.
Wave 3 - Hard
You need to be careful with Chaos Sorcerer. He might have "Magician of Black Chaos" in his Deck as his combo finish. Understand the effects first of Chaos Sorcerer, and if happens, use Force Focus's effect immediately. In addition, you must have Trap Cards that DO NOT destroy by battle or card effects this turn (e.g. "Impenetrable Attack").
If you succeed these three, then you're next to face the tougher opponents.
Good luck!
- 15th Floor Guardian
You can set up your board before Chaos Sorcerer appears. There’s time to put Force Focus but it’s cheaper to put a Chaos Hunter on the field, locks him down.
An easy method is just use Destiny Hero Plasma. At the first stage try and get Plasma in your hand (Stratos can help). Then have 3 monsters on the field and beat the first wave. Skull knight then appears and will either destroy one monster or be blocked. Then fill the slot of the destroyed monster and summon Plasma. Absorb Skull Knight with Plasma. Now the third round can't banish due to Plasma.
I have been using an auto duel deck and have no problems in the entire event. Use Balance with 8x 4-star Fire beaters, 6x equip spells, 6x battle traps. The opponent can't beat your monsters in wave 1 & 2, and the wave 3 boss monster will die with your battle traps
(Half counter is a perfect replacement for mirror wall)