Voiceover lagging after pairing watch with new phone

I have a 6, but did experience some problems after pairing. Mine were more siri related, rather than Voiceover, but there was some spill over. I had used the South African voice on my phone for Siri, and this seemed to cause some issues with the watch downloading the proper voices. Things seemed snappy enough, but Voiceover was not giving me the option to change synthesizers. I eventually figured out the issue was related to the dialect, which it thought was a language problem but whose splitting hairs. Once that was all set, the watch did work on downloading the correct synths.

I rebooted, after getting the correct voices, and that's when I had a problem. When the watch booted up, it was very slow. I had trouble even using it to enter a password. Once I did get it unlocked though, it seemed to have fixed itself after a few minutes. It switched all the voices, Siri and voiceover once unlocked, but after a few minutes, they just reverted, and everything seemed to be normal.

So while that's not an exact duplication of your problem, it had some sluggish elements. All of this happened Friday, so if yours were going to just, sort itself out, I would think that would have happened. The only suggestion though is to see if you can force a download of a different synth, and see if that helps. If your preference is Samantha though, maybe changing it, getting that all straight, and then changing it back might kick it into action.

I experienced exactly the same problem as you. I unpaired and paired my watch a number of times. Finally VoiceOver worked as expected but I discovered that my default watch face had been replaced by another one. Perhaps you could try deleting your current watch face and replace it with another one. It could be that the watch face somehow got corrupted.

did you setup as new watch or you restore from A previous backup.