I'm curious - how old are the systems you're working on?
In my experience, unit tests don't catch many bugs when the code is fresh. But when it's five years old with many modifications over the code base, some dumb little test that you thought was a waste of time is now alerting you to what would have been a horror regression.
In other words: Even though it feels like it's slowing you down now, if you write tests while the functionality is still fresh in your mind, and you capture your assertions well, they'll pay off dividends in the future once you've forgotten what some block of code does.
In my experience, unit tests don't catch many bugs when the code is fresh. But when it's five years old with many modifications over the code base, some dumb little test that you thought was a waste of time is now alerting you to what would have been a horror regression.
In other words: Even though it feels like it's slowing you down now, if you write tests while the functionality is still fresh in your mind, and you capture your assertions well, they'll pay off dividends in the future once you've forgotten what some block of code does.