It took 24 months of effort to get a particular system to barely run every hour by some contractors. After 3 weeks, I rewrote most of it and still have a month

It took 24 months of effort to get a particular system to barely run every hour by some contractors. After 3 weeks, I rewrote most of it and still have a month left, but it runs in 5 seconds. I'm having trouble right now convincing my boss it's better to work on the 5 second version even if he spent hundreds of thousands of dollars on the 1 hour version. It's the most annoying sunk cost ever.