The average worker in 2015 wanting to attain the average living standard in 1915 could do so by working just 17 weeks a year, one third of the time.
What proves this (or disproves it)?
It's true in the USA in the sense of the article A Glimpse of Your Expenses from 100 Years Ago:
Take-home pay in 2015 vs. 1915. Census Bureau data show that the median household income, measured from 2009 to 2013 (the most recent data available), is $53,046. Back in 1915, two years after income tax came on the scene, you were doing about average if you were making $687 a year, according to the Census.
Today, that $687 would be comparable to earning $16,063 a year, according to an inflation calculator on the Bureau of Labor Statistics' website. So Americans' buying power has improved considerably in the last century.
See also the US Bureau of Labor Statistics article The life of American workers in 1915