In the designation 15/15, the first number is your skill level. The second number is your skill cap. Your cap goes up 3 pts for every adventuring level you reach. To craft cured leather, you need a skill of 25. You'll be able to get to that when you reach Lvl. 9
When more of the Crafting system gets implemented, your cap will no longer be determined by your adventure Lvl. The current state is just to get Crafting up and running for testing.
