Nothing to take away from the original posters work. He indeed might have written that much code.

But in most cases. Its not very difficult to write 1.5 million lines of code for any project if you are writing code of the style AbstractClassFactoryFactorySingletonDispatcherFacadeInitializer

That sort of the code is basically 90% auto generated by the IDE. You write the remaining 10%.

As a matter of fact I would find it a tad little hard to believe that some one wrote that much(1+ million LOC) and didn't find a way to template it or do some metaprogramming work.

Patterns always emerge from that kind of pile.

The IDE can generate "headers" for a new file, it's not gonna generate tens of thousands of new files by itself, let alone in a meaningful structure.

I don't think a developer would write a million line at work in their entire lifetime.

I'm not saying it's impossible to achieve. I've seen outsourcing agencies deliver 100k lines with just a few block copy/pasted many many times, but that's neither working nor maintainable software.