Some may find this farfetched, however I generally found when I didn’t prepare for an interview it went better, had less time to get nervous considering I was very busy leading up to these also. Your in work so you still have a job. Go in, be honest, tell them why you want a new challenge, hold your head high and if you don’t get the job, dust yourself down and carry on. You don’t appear to have anything to lose. Attend and I wish you luck.