How often do cops shoot rifles? 
Up until about six months before I joined, every single officer in the history of the RCMP was trained and qualified on rifles.
The more insightful question is "what is the greatest fear of a cop who patrols a rural area?"
And the answer is "responding to a call and driving up the looong open driveway from the highway to the house, and being worried about the possibility of the unstable fucker with a rifle taking me out before I can even think about drawing my sidearm"
Or, put another way, to change your statement of "Handguns can hurt people just as well as a rifle, especially at a distance of 15 ft." to make it truthful:
"The only chance in Satan's fiery hell that someone with a handgun has a chance of winning an encounter with someone with a rifle, is if they are within a distance of 15ft." And even then, the guy with the rifle only needs to scored one shot to win, while the guy with the handgun might have to unload half a mag before the other guy drops.