Agree with what everyone say's.
If you are comfortable with CI, stick with it. You would need to spend time learning a new framework, which can take a little bit of time, especially If you don't understand design patterns.
Laravel uses design patterns quite heavily, so If you did want to move to that framework, I would suggest you start learning them first.
Dependency Injection and how IOC containers work will help you get a better understanding too.
The problem with Codeigniter is you basically have to hack it, somewhere along the line. It's difficult to unit test, it doesn't play nice with composer because of namespacing/psr etc.
There are workarounds using closures but it gets messy/hacky.
If you just wanted to build an API, I would suggest Lumen, Laravels little brother.
Good luck