I had a very similar experience in another enterprise storage company with a code base of ~6M loc of C/C++ and gazillion test cases. Originally, it used to take roughly about an hour to just build the system where it did a bunch of compile time checks, linting etc. Then if everything goes well, it goes to code review, then to a set of hourly and nightly integration checks before it gets merged to the main branch. It would take another cool 3-4 months of QA regression cycle before it gets to the final build.