I agree, depends on the doctor, how strict/busy they are and how complex the issues are.

I have an ongoing health issue and have to see my doctor very regularly. He knows that it's starting to cost me a fortune so he has said he will bulk bill me if it gets to be a strain. Because I am aware that his time is valuable I try to keep other issues very brief. For example my DS injured his ear recently too and needed the doctor to have a quick check in his ear. This only took a second or two so my doctor didn't mind as I was (in total) well under the 15 minutes. You have to use your discretion. Keep it quick if possible if you want to get two for the price of one... and ask first if it's ok to ask a quick question.