The WT yearbook stats for years 1988-2014 are available at the jw.org official site at:
Toward the bottom of the page is the link to download the excel file with all the stats. I wasn't aware of it until yesterday. Expecially interesting is the one called 'Yearbook Stats by Field' which makes it easy to compare across years.
A few observations about the 2015 figures, when added to the file (the file only goes back to 1988, so my comments below reflect that limitation):
The ratio of peak publishers / ave publishers is the lowest from 1988 to 2015
Number of baptized is lowest since 2005.
Increase in Peak publishers is lowest from 1988 to 2015
Increase in Ave Publishers is second lowest from 1988 to 2015
Number Baptized as a percent of publishers is lowest from 1988 to 2015 <edited to add
Interesting, but the question I have is, Why don't the columns add up to the published Grand Totals? It's not just one or two, but none of the columns are summed correctly. For instance, the 2014 total of baptisms Grand total is given as 275,581 but adding all the countries separately gives 276,122.
It is apparent that the published Grand Totals are excluding something but it is not specified.
Maybe their using that 1914 math again.