"P 115 is a 3-4th century copy of the book of Revelation that was discovered at Oxyrhynchus in Egypt – the source of very many papyrus finds of all sorts, secular mainly, but occasionally, as in this case, biblical. P 115 consists of a number of fragments / scraps (several dozen), which, taken altogether, contain somewhat more than 1% of the book. As I say, these are fragments, and as such leave much to be deciphered in studying them. For this particular fragment mentioned by the individual you cite, it is true that we have the Greek short-hand for the number 616. But there are a number of factors to consider before jumping to the conclusion that such is the "proper" number of the beast:
1) This papyrus is later than the best copy we have of the book of Revelation, namely, codex Sinaiticus (aka "Aleph"); that complete copy of Revelation reads "six-hundred and sixty-six", and
spells out the number fully rather than using Greek numerical short-hand (a method which is often problematic as all scholars are aware). Sinaiticus dates to the late second or early third century, so is about a century earlier than the papyrus, even should we wish to accept the early dating for the papyrus which Greenfell and Hunt give it.
2) Since the papyrus uses Greek numerical short-hand (i.e., the letters/symbols 'chi-iota-stigma' as opposed to 'chi-xi-stigma'), there is a much greater chance that it is the papyrus that is error rather than the manuscript. That is because the Greek numeral notation system was far more problematic than our Arabic numerals (for reasons that would be too time-consuming to go into here). Suffice it to say that numbers are always viewed with some suspicion in all of Greek textual criticism for precisely this reason, namely, the short-hand use of a system that was easily mistaken or altered in transcription. It is true that one ms., "C" (Ephraemi rescriptus), also has this reading, but this only shows that the papyrus, a cheaper sort of text, was probably derived from "C" or a related patrimony.
3) There are good theological reasons for preferring the traditional reading. In a nutshell, six-hundred and sixty-six falls just short of a perfect "seven" in a repeating cipher, and is therefore an apt identifier for the beast who will seem so close to being the Messiah that he will be able to fool all but the elect. On the other hand, 616 means nothing.
4) What has been missed by all commentators, as far as I know, is the fact that the Greek word for "six-hundred" in Aleph, the only one of the three words in the compound numeral which declines, is actually in the feminine gender (most texts incorrectly print the masculine). This is a striking development which would catch the eye of anyone reading the whole number for himself (since it begs the question of what the number then agrees with grammatically), and would make the chance that there had been an error very unlikely in any manuscript which preserves this reading (as Aleph does). On the other hand, this piece of information is entirely lost when the short-hand method is used. What that means is that any ms. tradition going to the short-hand from the fuller version necessarily changes the text by losing a key piece of information (even if the otherwise correct 666 is retained). For the meaning of this feminine ending and also for the theological significance of the numeral related thereto please see the link:
"The Number of the Beast" in CT 4.
5) Finally, there are other problems with the text of the papyrus. In this fragment the letter which should precede the numeral (i.e., an upsilon from the word for "of him / his [name]") is not in fact what we find. Instead we find an eta, and this cannot even be easily explained by the other words in the context. What it could be, however, is the Greek word for "or", so that what we very well might have here is the papyrus retaining an alternative reading:
"[his number is 666]
or 616 [depending]"
The fact that the 616 follows the "or" makes it clear that whoever copied the book felt this alternative to be the less likely reading."
Antichrist: the Mark, the Number, and the Identification of the Beast