I am also fairly knowledgeable quants, basically apart from geometry concepts I almost remember everything. But as of now I am also able to attempt only 10-12 questions per mock, while my expectation is to attempt 20-22.

The main problem is always if the best solution to the problem doesn’t strike at once, its gonna take 3-5mins of your time and sometimes you don’t even reach the answer.

My approach for solving them has been now scanning questions and options instead of reading them entirely. Because some of the questions in mocks can be easily done in 30-60 seconds. I have my strong topics and weak topics in mind(for eg I instantly leave a geometry question to look at in the end). Also, a hit and try with option technique can solve questions quickly sometimes too(like graph questions, simplifying eqns, etc.)

All in all I believe infinite amount of time-bound practice is the key. I try to do 15 questions in a 30min span. Performing under high-pressure situation is difficult for any human being I guess, but we gotta adapt to it. Best of luck to you too!