I deal with this constantly. Profilers are your friend. I keep begging my team to use the database dumps from production to test with, but nope. Don't feel bad about messing up though. The amount of fuck ups I deal with in prod is exasperating. At least most of the things I break is a quick 5 minute fix and not weeks of rework.

The hardest thing I have explaining to the team is the concept of time. Once you have done controls programming and get to witness how much happens in 50-100ms, it sinks in. Your thing takes 500ms? 1 second? They think this is acceptable on something that is dealing with less than 100 database records. 😭