I am planning to visit Italy in December 2019. The visa appointment date for Schengen tourist visa at Italian San Francisco consulate that I got is just 12 calendar days before my travel date. All slots before that were booked. Are 12 calendar days enough to get my passport back? Is there a way to expedite request?
The Italian consulate is required to give you an appointment within two weeks. The way you describe it, it looks like they are ignoring EU rules.
In your case, I would contact the consulate and perhaps the embassy.
Contacting them now will also help you to prove that you actually tried to make an appointment early. When you hand in your application, they are required to tell you whether there is enough time to process it. Pointing out that you tried to get an appointment several months earlier might convince them that they should process your application quickly. I believe this kind of proof should also be handed in with the application to make sure the processing visa officer sees it.
The limits and rules by which Schengen visas are issued are all in the Schengen Handbook (Handbook for the processing of visa applications and the modification of issued visas).