We all know that advancing ignition timing makes a difference. My question is if I should advance mine more.

Heres the situation:

I used to have my ignition timing set at 18 degrees, and it had slight pinging, that was when my knock sensor was broken. I set timing back to 15 to be safe. Now that I fixed my knock sensor, i brought timing to 18 degrees and there is no pinging at all. Should i advance more? I heard that You should not go above 18 degrees. Thanks for all input.