Torah says you need 2 witnesses to establish a matter, and I only know of 1 that fixes a year for Jubilee. So it is not exactly at Torah standards. Rambam (Maimonedies) said the destruction of the second temple happened in the 15th year of the 9th Jubilee (yovel) period. This would have meant that 55-56 AD was a Jubilee year and therefore the next one at Tishri 2015 to Tishri 2016.
What source did HE use? I don't know. Could he have been wrong? I don't know. But he probably had better sources than me. If someone thinks they know of a better source from an older time period, I'm all ears.
However the good news is that establishing the 7 year Shmittah cycle is not very controversial at all. We do know that one quite well.
From: "Paul Wilson"
what proof do you have that 2015 is a jubilee?? have previous jubilees been declared?? or is all you have ‘something happened in a certain year so it must have been a jubilee’?? that is really conjecture. surely if this year is a jubilee there is proof beyond conjecture?? the jubilee would have to be counted from when first instituted. JR Church's book shows a good timeline and he shows the 2015 year as sabbatical not jubilee. see http://www.fivedoves.com/letters/jan2012/paulw110-1.htm. even if you were to start the jubilee count from a modern date how do you choose which date is the start point?? not all significant dates for Israel occur 50 years apart.Paul