Just a warranty figure
The 150 or 300 TB figure is just for the warranty. Anandtech have a good write up on this here http://www.anandtech.com/show/8239/update-on-samsung-850-pro-endurance-vnand-die-size
They reckon that for a worst possible case the 1TB version would withstand 430GB per day for 5 years.
The old 256GB 840 Pro managed to clock up 2.1PB in the tech report test http://techreport.com/review/27909/the-ssd-endurance-experiment-theyre-all-dead/2