As a stutterer, I never felt like my stutter ever really hurt me during interviews. The only times where it hurt me was when I felt to nervous to speak and ended up not saying much. As long as you make an effort, you should honestly be good. When it comes system design, diagrams are your friend. It's almost like having a cheat sheet when it comes to stuttering as if you have a really good diagram, you don't really need to say much. And drawing the diagram gives you a bit of reprieve if you need a break from speaking or if you find yourself stuttering a lot and you need a quick breather. I stutter pretty hard sometimes. And I can confidently say many engineers who do not stutter communicate a lot worse than I do. So if you keep making an effort into building you communication skills, which you definitely are, you'll look better than a lot of engineers out there. In many ways, stuttering has helped me excel in technical leadership roles because it caused me to really focus on my communication skills since it's an area I was particularly weak in.