When you are reborn, your items will be reborn with you. However, they will revert to low level items again - otherwise you wouldn't be able to use them any more.
If you don't want your items to be reverted to 15th level, you can unequip them all before talking to Eternity in the marketplace. Those items can be kept in your warehouse for safe keeping until you are ready to use them again.

Caps, Hats & Helmets: Will revert to a Destiny Cap (Level 15), a Badger Hat (Level 22), an Iron Helmet (Level 15), or a Guard Coronet (Level 15) depending on your new character class.

Armor, Coats & Robes: Will revert to a Tao Robe (Level 15), Ox hide Armor (Level 15), Leather Armor (Level 15) or a Deerskin Coat (Level 15), depending on your new character class.

Bracelets, Rings & Bracers: Will revert to a Peach Bracelet (Level 15), a Porcelain Ring (Level 13) or a Copper Ring (Level 10) depending on your new character class.

Bags, Earrings & Necklaces: Will revert to a Flower Bag (Level 17), Heart Necklace (Level 17)

Boots: Will revert to Ox hide Boots (Level 10)

Shields: Will revert to a Soft Shield (Level 40) If reborn with a Shield, it will automatically be stored in your inventory.

Bows: Will be reverted to a Mulberry Bow (Level 20) The level of the arrows will not be changed.

Weapons: Will be reverted to the appropriate weapon of lower power (level 15)