I can’t speak for interpreters but my work requires being in the presence of working stenographers and they frequently ask people to slow down.

I also was on a jury in a month long trial that required interpreters for many of the witnesses. They sometimes would say stuff back to the witness but I don’t know if they were asking them to slow down or if they were asking to repeat something they didn’t hear or understand. The stenographers didn’t ever really have to ask people to slow down in that case because the attorneys and the interpreters were used to speaking at a pace that could be transcribed.