What 16 hour work day? The average Japanese worker worked 1719 hours in 2015, that comes to about 7,4 hours per day, five days a week for 46 of the 52 weeks. For Korea the same figure is 2113 which comes to 9,2 hours on average (assuming a generous 6 weeks vacation/bank holidays etc).

The highest of any country last year is actually Mexico with an average of 2246 hours per worker and year. I went 15 years back just to make sure, the highest Japan has been in that time was 1821, the same number for Korea 2512 (10,9 hours/day).

The highest Korea has ever been was 2911 (12,7 hours/day) and that was in 1986, since then the average workday has steadily become shorter, the same is true for basically all industrialized nations. The highest figure ever recorded for Japan was 2243 (9,8 hours/day).

I very much doubt any industrialized nation has ever averaged 16 hour work days for any period of time and I can find no recorded statistics to disprove that assumption. I can tell you for certain that neither Japan nor Korea has ever been that high. However, if you want to dig further here's a damn good place to start:

Average annual hours actually worked per worker, OECD statistical database