I've just realized that recently beneficiaries (IR-1) from countries in Latin America and Africa need to send DS-230 part I and II to NVC, along with translated police documents and birth certificates. Some months ago beneficiaries only needed to show part II during consulate interview with documents in the original language. Will these changes make the whole process (NVC+consulate interview) slower or faster?

Neither, the changes don't affect the time it takes the NVC to process everything. It does make it easier on the CO because they send all the info to the embassy directly instead of the beneficiary having it on hand at the time of the interview.

It should not affect the length of the process. It is just different for each country. Some countries' Embassy require visa applicant bring DS 230 part I, part II, police certificate, marriage certificate, etc during the interview whereas for some countries, these forms, documents should be sent to NVC.