It has been random but with high frequency, that download speed for Apps updates using itunes are extremly low. I checked my internet connection downloading other files, watching HD videos from youtube, watching netflix and other test to discard my internet connection. The issue is only with iTunes and specifically downloading Apps.
Router/modem have been restarted several times, I have wired and Wi-fi connection, both has the same behaviour. It is not always, but in last 2 weeks, at least four-five times this had happend.
Different ours, different days, it is just randomly that a 25 MB App update takes more than 8 minutes downloading, that normally takes 50 seconds or less.