Myth 18 Some languages are spoken more quickly than others.

Some languages and accents do sound faster than others. There are a few different characteristics for measuring the differences in speaking speed.:

 

 Measures of speaking in different languages

One way of measuring the speed is by measuring the number of syllables that someone speaks in the time they are given. The issue here is that incorrect pronunciation can mess up that process. Osser and Peng has also measured sounds produced per second, but after comparing that to different languages the overall differences were too small to count it as actual speed difference.

 

Speaking rate as an illusion

The impression we have of languages being spoken either faster or slower may depend on their characteristic rhythm. It’s based on whether a language seems to be stress-timed or syllable timed. Many studies have been unable to confirm that this plays a role.

 

Social and personal factors and speaking rate

Social factors play a role as well, some interactions prefer slower speech while others don’t. There are also speakers who are naturally fast speakers, but others may speak slower when they are tired.
Every language has its own personal and social factors on the speed of speaking the language.

 

I am a naturally fast speaker and whenever my family points that out my parents just tell them "Oh that is just how Dutch people talk." so that might have influenced their entire few on the language. 
As I've mentioned earlier, your understanding of a language might have a huge effect on this, just like the flow of the sentences. So (smooth) pronunciation plays as much of a role as the people in question speaking/understanding the language they are judging.
Every language has people who speak fast and slow, it isn't always easy to figure out what the standard is. People will always have their own opinion on these things and even if it is proven that all languages are spoken in the same speed, there will always be people who say that some sound faster than the other.