Yes, any time there is a double consonant, it is pronounced longer, kind of like how English has short vowels and long vowels. These double consonants can make a big difference; for example, «capello» = "hair," but «cappello» = "hat."
Forvo is a great website to hear pronunciations. Here, you can listen to how «vero» sounds; I would suggest listening to the «Strano, ma vero» and the «a dire il vero» audio to get a feel for how short the «v» is in those words. Now, here you can listen to the «davvero».
Also, even though «sc», the «gl» in «gli», «z» and «gn» are never written as double consonants inside a word (e.g. the word is «lasagne», not «lasagngne»); they always sound like doubled (or long) consonants. This is discussed in this Wikipedia article in the first bullet point under consonants; the word for doubled consonants is geminated consonants. I hope this helps.