Maybe they just renamed Coruscant, just like they renamed everything else that is otherwise exactly the same 😃 Hopefully, we’ll learn more about these things in The First Order Strikes Back 😉
No, the Hosnian system (and Hosnian Prime) are not Coruscant. I believe both some of the “Journey to Episode VII” stuff as well as the TFA novelization reveal that the seat of the Senate is on rotation, elected every so often, and that at the time, the Senate is at Hosnian Prime. But it is one of the Core Worlds, apparently. Odd, I know.
I’m generally not big on noevelizations, but I think I might have to give the TFA one a read.