I live in mountain, where there is only low speed internet connection, it did take 3 hour to download the Avast version 6.0.1125.0 , so I would prefer not to download Avast again.
You should use a free download manager, so to reduce the possibility of corruption of the download file.
Using a well known repository as near to your area as you can could improve your chances of getting "the correct file".
In addition, filehippo.com has older versions too, JFYI.
And I'm french speaking and it's easyer for me to use the french version of Avast, the link you give me are the english version.
Even if you install Avast using the English installer, you can change/add the language afterwards from Avast settings -> Language.
There is an additional alternative, but I can't assure you that the problem won't come back again.
The complete database can be downloaded too, instead of the program+database. From the 2 options, I would recommend downloading the complete program, but the database alone is there. It is still around 30MB, which is much more than the usual download (around 200KB).
But before downloading anything, I'd like you to check:
Avast Settings -> Updates -> "UPDATE PARAMETERS" -> "I only connect to the internet using a dial up modem". Save the settings and REBOOT.
Since you have a low band connection, maybe this setting is your solution to normal automatic database updates (which is around 200KB or even less).