Houston, we've got code quality problem here

Let's say you have a rather old project (about fifteen years old), and a few developers working on it. Today, there are no special practices regarding code quality, at least the bare minimum (code review and PR are still in their infancy, no CI/CD etc.). This creates technical debt on the one hand, and bugs on the other - in short, a whole host of things that your developers will have to work on rather than features. If you're the technical director or project manager on this project, at what point do you say to yourself "wow, this is serious,
