I've been in over a dozen Ayahuasca ceremonies, and done lots of other shamanic healing with various other plants, mostly for healing of illnesses. I have tried to ask the spirit of the Mother Ayahuasca to heal my stutter but it's never happened, so I've come to the conclusion that my stutter is just going to be part of who I am and my larger purpose in this life for better or for worse. As to whether it has improved my stutter immediately after, it's quite unpredictable given that each ceremony is different, sometimes yes and sometimes no. Also factoring in that I was mostly speaking my third language, Spanish, that I am not entirely fluent in and tend to stutter more in. But of course everyone is different. We say with Ayahuasca that she gives you what you need, not what you want. I think if you feel called to try it there's no harm (with the caveat of doing your research beforehand and finding a safe and reliable place to do it!), and it will probably yield some deeper insight about this or life in general. With the medicine intention is important, you could set an intention to improve your stutter and see what happens.