Hi duybachhpvn,
On the Official GMAT, it's certainly possible that you might see three RCs in the first 20 questions (although that's not guaranteed to happen - you would probably see two though). Fifteen SCs is on the high end, but it's also possible (especially when you consider that there will be Experimental questions - questions that are in the 'testing phase' and that do NOT count towards your Score); you'll likely see 12-13 SCs. Ultimately, the exact number of questions that you'll see of each type (or when they might show up in the section) shouldn't be what you're focused on. Assuming that your Goal is to score at a high level overall, beyond having the proper Quant and Verbal knowledge, you also have to train to handle each question type in an efficient fashion.
Before I can offer you any advice for your studies going forward, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) How long have you studied?
2) What study materials have you used so far?
3) How have you scored on EACH of your CATs/mocks (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
4) What is your goal score?
5) When are you planning to take the GMAT?
6) When are you planning to apply to Business School?
7) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich