I can't remember which exact area you're referring to, but in general you will see that sorcerer types cast too much for you to interrupt it all, so you have to learn what to interrupt and what not to interrupt. Also, remember that you have more tools to deal with casts than simply your class-based interrupt. Running away quickly and then force leaping onto the enemy will give you focus and interrupt the cast, and any stuns, mesmerisms, pulls, pushes, etc. will too. These can buy you time for your interrupt to finish its cooldown.
For the JK class quests, managing interrupts is a must, I'm afraid. Good luck, and I hope this helps!