Hi, I was on olanzapine my dose was anywhere between 5mg and 12.5mg. I felt a lot better on seroquel after the transition period. I find I am not as drowsy and my appetite isn't as strong, meaning that I am not gaining as much weight. Olanzapine is good for crisis but day to day I find seroquel suits me better, hooe it goes well for you too!
I was in the same situation about a year ago and there weren't any issues. I asked my doc about it and she said that there wouldn't be problems because they were both AP meds.
I am no Dr. but if that's what your doc said to do...it is probably fine. If you don't feel comfortable you can always ask him/her to ween you off of the olazapine slowly.
But, seroquel is a strong drug..so, I think you will be fine.
But, again, I am no dr.