New Hampshire is part of the Drivers License Compact (DLC) while Massachusetts is not. This Compact requires member states to report back to the licensing state of a motorist any moving violation convictions. Massachusetts while not a part of this Compact does have agreements with other states to share moving violation convictions with the home state of motorist and receive this information in for MA drivers.
Since likely Massachusetts will report this speeding ticket back to your home state of New Hampshire, once you plead guilty and pay the find thus being convicted of the offense, it will be up to the NH Division of Motor Vehicles and state laws if this out of state speeding violation will be placed on your driving record.
The Drivers License Compact is discussed in Chapter 263 of the NH Statutes but does not specifically state if out of state infractions will be placed on your NH driving record. However, the New Hampshire Administrative rules give more information on this topic.
Saf-C 212.02 states that any person convicted under the laws of another state, of any violation which would have constituted a violation specified into Saf-C 212.03 if committed in New Hampshire, shall be assessed the number of points specified in that section.
You can go through this section that lists the assessment of demerit points to see all of the points assigned for various violations of motor vehicle laws. The one that applies in this situation is speeding when the conviction is for speeding under 25 miles per hour above the posted speed limit. This speeding violation is assessed 3 points under NH law.
Since points appear to be assessed for out of state violations then it would also stand to reason that the MA speeding ticket would also be placed on your driving record along with the demerit points.
The NH DMV does not state how long violations stay on your driving record but do note that points stay on a person's record for 3 years. Points are divided by each calendar year thus if an individual receives points in the year 2007, the points will not count on his/her driving record in the year 2010.
While we do not know if it is common to receive a ticket for 15 mph over the speed limit in the area of Massachusetts that you received the ticket we can say in general if you are going on5, 10 or more mph over the posted speed limit you will typically get ticketed by law enforcement.
As for how this speeding ticket will affect your auto insurance really depends upon your insurance company's rating system. Since this MA ticket will likely be reported to NH and placed on your driving record your insurance carrier should see it the next time they pull your MVR. At that time their rating system will dictate if your rates will be raised or not.
To find out about your insurance provider's rating system check with your agent and/or the NH Insurance Department with whom insurance companies must file their rates with.