your 750 was a damn fine piece of machinery "right out of the door". How long it will remain in running condition and how many miles can be gotten out of her will depend mainly on you--- how you ride (it's a cruiser, not a crotch rocket), how well you maintain her (a little TLC goes a long way) and how much pride you place in her.
Before I get too old and decrepit, and barring any catastrophic circumstances or idiotic blunders on my part, I fully expect to get at least three times the mileage out of mine than is showing on the odometer now. With only fifteen thousand miles on your bike, I'd say that you haven't even gotten her fully "broken in" yet!
So, take care of your bike and enjoy the ride.
'02 VN 750
stator replaced @ 50,570 miles
forks rebuilt @ 58,900 miles
currently on third battery & sixth set of tires