The word 'ganz' puts emphasis on what you said, like the word 'sehr'. The prefix 'ur' has the same function, but is slang, used in Eastern Austria. Urklein, ursuper.

It's a bit like "suddenly" vs "all of a sudden" in English. They mean basically the same, but the longer expression shows the level of surprise caused by that sudden event. So usually we say "plötzlich", but when you want to emphasize that it was absolutely unexpected, you can add an extra syllable and make it "ganz plötzlich" or "urplötzlich".