I saw the following phrase in an article, written in this year:
Because the full form of d.J. is dieses Jahres, would that mean October 2016?
If I wanted to mean October 2015, can I write v.J. for voriges Jahres?
Yes you can. v.J = vorigen Jahres - see the usual abbreviations from the following list (from Duden):
But anyway I would prefer Okt. 2015 instead because it will not expire next year :)
This is - as so often - a matter of context.
If the author writes about current events, yes, it could mean October 2016.
However, if the article describes something happening in, say, 1961, d.J. would consequently mean October 1961, even if the article is published 2016.
Unfortunately the snippet you give does not allow a definitive answer.