Can you slightly slow down your speaking ?
Is this sentence written right???
It's written OK, but it sounds unnatural. "Could you speak more slowly, please?" would be a better alternative.
You could say.....
Could you slow down slightly please.
You don't have to include the verb 'speak'.
Do you think you could slow down please?
Please slow down. I don't understand.
Can you speak slowly?
There are many ways you could say it. :)
Sincerely,
Tutor Stephy