Keep playing around with the values to get the quality you need. Add higher samples value to reduce grain, just keep in mind this increases render time. (Increase to 32, 64 or even 128). When you're happy with the result save the image and open it in Photoshop.

Step 3: Add AO Layer in Photoshop

To avoid the Ambient occlusion layer darkening your image in general, you might want to adjust the image levels (Ctrl + L) before you apply it to your picture. A quick auto adjust should do the trick (Fig.09).




Now all you have to do is to drag the Ambient Occlution Layer on top of your final render and choose Multiply. And voilà, you have Ambient Occlusion that was super quick to render with the added advantage of being easy to tweak and adjust (Fig.10).


The final result can be seen in Fig.11.


And for comparison, the render before Ambient Occlusion layer was applied (Fig.12).

Thanks for reading!