Each bookshelf increase 2 level of requirement. In vanilla, the maximum level of the Enchantment Table is 30.
In SkyBlock it is increased to 64, and can up to even more when replacing normal bookshelves with Enchanted Bookshelves.
Skyblock's enchant system is more similar to Minecraft 1.7. You'll need to spend exact level that show on the preview to get the item enchanted, but it doesn't require Lapis Lazuli.