I think for most people Keyhole and TFE take the longest. I suggest you carefully review the solutions for your first three exams and from there see how you can improve your speed. The solutions often tell you how to approach the problem so you can solve it quickly. Also, determine why you were stuck on a certain question and try to avoid making that mistake on your next practice tests. And if you're spending too much time on a question, make an educated guess and move on. There's more forgiveness on the PAT section relative to the other sections.
Getting an 18 on BC PAT is not bad at all. Just make sure you review your mistakes carefully and keep on practicing. I was averaging ~19 on my first few practice tests and was getting ~20-22 on the last few BC PAT exams (7-10). Ended up with a 25 on the real thing.