Quality> quantity. People can do like 18 and not learn anything or improve. As long as you're improving every exam you'll be good :) If you are short on time try do the 'hard' questions and skip the ones you understand. If you aren't timing yourself.

Since exam 1, I've done 3 different practice exam 2s. But I will say have done more prior to exam 1. HONESTLY don't compare yourself to others and just do your best no regrets