Take 10 was you could treat the dice result as if it were a 10 in situations where your character wasn't under pressure. It was a way of making sure a grandmaster with decades of experience wasn't messing up simple tasks absolutely constantly. If you had a modifier of +5 or above you would always succeed an easy check with a DC of 15. It stopped those ridiculous "How do you miss a volcano" situations.
If it's a simple (or very easy) task, the DC should be 5 - or there shouldn't be a skill check at all. You don't need to roll a skill check to walk on even ground or to open an unlocked door. You only need to roll skill checks in situations where there is a reasonable chance of failure. There is no easy check with a DC of 15 - that's a moderately difficult task.
