You spend 17 mana for nothing but keep the enemy in his zone?
Let's assume it works. Usually the enemy uses his first turn to deploy a Creature or at least one conjuration.
He's caged, so he can deploy the creature and only one conjuration. In the end, it's not a lost turn for him.
Maybe he can already attack one of the walls with a melee attack. The walls have no armor, so there will be some damage.
In round two, you'll have 11 Mana, not enough to deploy a good ranged creature and use your second action in a way that it makes sense. I would say: lost turn for you.
The caged enemy can deploy a creature, that will start to tear down your wall in round 3 and is still able to cast a useful equipment or something like that.
In Round 3, the trouble starts for you, because you cannot keep the enemy in his cage. He can melee attack the wall and use his quickcast to teleport his mage or his creature out of the starting zone, just to be sure not to end in a cage again.