I am really, really, really, really, really, really, really enjoying this game. It's much more clever than your typical RPG, with the unique way the story unfolds and using gems as a form of currency that can upgrade your Crowns and Equipment (yes, you'll eventually find a shop that can upgrade your equipment by using gems) or get sold so you can buy new items.
As restrictive as 15 slots per character sounds, as well, you can't use more than five types of Magic or equip more than four items at once so you will always have 6 slots per character free to carry consumable items and loot.
Plus there's the fact that, because your party is seemingly always so small (I've not had a full party of four since beating the Witch at the beginning of the game, most of the time there being only two per party), you have to carefully select what Crowns everyone uses.
All in all, the game really has improved over my initial impression. At first it seemed excessively restrictive in an attempt to simplify the game mechanics, but this game is far more clever and technical than I thought.