It's a pretty realistic expectation for a mediocre locksmith in the real world faced with the average door lock. It's a bit slow for the fantasy expert lock picking thief who's invested their ability and skill increases to excel at a mundane and achievable task. But time spent is the smaller issue.

And it's 3 gp a thieves tool set, but the bigger issue is bulk. God forbid you've a dozen doors with good locks in a dungeon, that's 4 bulk worth of picks to get through--pretty much the thiefs whole inventory--and a 50 percent chance of ultimate failure (not to mention 240d20). Pretty rough on the class fantasy. If nothing else I'd change the names of the locks to pad the thief ego: poor becomes average, average good, good master and master legendary. I don't want my player stymied by an average door because he only brought one backup toolkit.