The answer is: Fifteen cold years have passed and I still think of my beloved as if he were alive.
In this stanza Emily alludes to the pass of time “and fifteen wild Decembers” since her lover died, she shows that many thing has change “From the brown hills have melted into spring” and “After such years of change and suffering!” however she also says that no matter how much time has passed or how many changes there has been she still remember him “Faithful indeed is the spirit that remembers”
