I'm currently on floor 19-ish in the big tower. Leave it to Falcom to go all out on the last dungeon!
More tips:
Level 9 is a breeze, basic fetch quests. It's a short level too, nice break from the dragged out previous levels.
Level 10 is pretty easy too, but there was a puzzle that took me awhile to figure out. Outside of the town, there are four pyramids in the desert scattered in a north, east, south, west fashion (the northern pyramid is one screen north and one screen east from the town, the other pyramids are four screens apart from each other). Each pyramid has two goddesses statues in front that can be rotated by pressing the action button.
The entrance for each pyramid is blocked by some sort of force. When you're ready to enter the pyramids (I believe you need to have the green haired character wearing a hat in your party for this), you'll need to change the direction of all the goddess statues to correspond in the direction of the pyramid you want to enter. For example, if you want to enter the western pyramid, change the direction of all the statues to face west. There will be a boss fight in each pyramid you enter, and beating them will give you four wind items.
After defeating each boss, change the direction of all the statues to face east (I might be wrong, but I'm pretty sure that's the direction). Go to the screen that's located in the center between all the pyramids and talk to your friends standing around the middle of the screen. There will be a cinema and you'll be transported to the next dungeon. WARNING: After you're transported, you can't go back, so make sure you're stocked up on vitamins!