It takes about twenty minutes at least to pray five decades devoutly (in English). According to Saint Louis of Montfort ( read the "Secret of the Rosary")racing through the Rosary is not pleasing to God,even insulting.
The Rosary in German takes longer, approx.25-30 Minutes for five decades. They repeat every mystery at each Hail Mary.
In Ireland people race through the Rosary at an awful speed, you can hardly make out the words,which the Archangel Gabriel adressed to the Blessed Virgin. In a little booklet,written by an irish priest I found the comment : It is easy to pray the Rosary every day, it takes only 10 Minutes to do so (!!!).
I often wonder if the Rosary is very effective if people pray it so fast.
Another practice I find quite awful, particularly in Ireland, is the very sloppy way people bless themselves with the Holy Sign of the Cross. You could not make it out as a Sign of the Cross at all. And, if properly done,it is such a beautiful sign and brings so many graces and blessings, and 100 days indulgence, 300 days indulgence when made using Holy Water.
In our resistance chapel here we do not say the Rosary publically before Mass as people come and go for confessions and also arrive at different times. However, on Sundays when there is no Mass, we pray the Rosary publically in the chapel, where the Blessed Sacrament is reserved, and it takes one hour to pray the fifteen decades. It is quite an effort mentally to do all the meditations of the 15 mysteries in one go.