What does the book say 7.5 is? An average portion? Or is that per 100g?
I had a look at syns online, and can't find the JO speciffically, but Pizza Hut spag bol portion is 16.5 syns on EE and Green.
If the book says 7.5 for an average portion in an Italian restaurant, then that might be more accurate considering Jamie's Italian is exactly that, and pizza hut isn't!
Sorry I can't be of any more help x