Hi @Debek,
I have been working with this in LRs text tool recently—and as far as I can tell—there’s no way to slow the TTS down—not there unless there is some shortcut I am missing out on somewhere.
I found this request related to the speed of TTS/the read mode/text tool. Here’s the link, if you want to check it out and put in your voice about the request:
Other similar requests:
I also found this old topic post/thread (March '21) related to Reader mode, but I’m unsure where they are currently on the TTS. (I’ll update if I figure anything else out.):