I was put on 300mg straight away after 5mg of olanzapine. It was for psychosis, but not hallucinations. If Seroquel or any AP is too high I have recently learned it dampens your mood majorly. They deplete the vitamins the brain needs like magnesium and b vitamins needed for energy and nervous system. So get yourself some supplements.
From being on forums for years I see how tough a time some people have in finding the medication that works, and the dose levels.
I got put on a CTO (Compulsary Treatment Order) it basically means sectioned. The doc was adamant quetiapine mustn't be working as I was suicidal, to the point I escaped the ward and sat at the highest peak of the hospital at least three times. I tried the most common APS - clozapine, respiridone, aripiprazole and after 8 months and ECT the ar$%holes put me back on the quetiapine that I started with so the whole detainment was just a dent in my life won't get back.
I will just end by saying that quetiapine is quite sedative but you can get used to it, I know it is hard. I also tried Amisulpride and never worked. Tried nearly all the popular ones. Quetiapine was always best but you might get different side effects.