15-50 being quite a big range and the 2004 publication date of the book (the comments hint at the reference being earlier) make me reluctant to take it at face value without looking into it in more depth, especially regarding new technology like TS, Rust, or enterprise Haskell.

Read it as 1.5-5% of lines contain bugs.

In the original post AirBnB said 38% of their bugs could be prevented by static typing. This would bring this to 0.9-3%. Not insignificant, but LoC is still more important.