Less than 15 over is as low as you can go for a speeding ticket and you don't get any demerit points (contrary to popular belief, you don't loose demerit points, you gain them). It's very tempting to accept this.
Many insurance companies count convictions, not necessarily the number of demerit points you got. Typically they are looking for three convictions which will put you in a higher rate. Most insurance companies send you a questionnaire in the mail around policy renewal time asking how many KMs you drive annually, do you drive to work, have you received any convictions... It's the last question that's trouble. If you say no, that's insurance fraud and they can deny you benefits later, even years later.
The last time I renewed my insurance I ignored the questionnaire, they sent me another notice, which I ignored and then I got my pink slip in the mail anyway. I know other companies will actually call you to ask you why you haven't filled it out.
Also your driving record will have the conviction on it. Every cop that stops you from now till the day you die will see it on their computer. It doesn't go away and you are more likely to get another ticket since you didn't learn your lesson.
This is just a guess on my part, and I know I'm going to get a reaction for saying it, but my experience has been that if the cop reduces the ticket at the traffic stop, they are less likely to show up in court if you fight it. They are doing themselves a favour knowing you are more likely to pay a lower fine and they don't have to show up in court or prepare disclosure.
On the top corner of your ticket, they can make a notation as to the actual speed you were going. Sometimes the prosecutor will threaten to bring the charge back up to your original speed. If you fight the ticket and the cop shows up, you can still plead guilty and pay the original fine. You've lost nothing but your time and at least you tried to avoid the insurance hit. And since the conviction isn't registered until after the trial, which can take more than a year in Toronto for example, you delay the conviction till after your insurance renewal date, so you can answer the insurance questionnaire honestly. (sorry for the long response!)