Hard to say without knowing what you are attempting to RE.

IIRC for a 10% success item, the odds of then next attempt being the first in 22 failures is almost exactly the same as the odds of the next attempt being a success. (9.85% vs 10%)

So a string of 15 failures wouldn't even be considered unlucky. Only 15 failures before success would probably be on the lucky side.

That being said, if it's a 20% success item, then the odds of gettng 15 failures in a row would only be 3.5%

So a bit on the unlucky side, but not terribly so. Considering how many items you (and everybody else) is going to be RE'ing, it's going to go on a 15 failure streak a WHOLE lot of time.