I have no GrimeFighter license.
Avast IS 2015 (Windows XP SP3).
Go there:
"Scan -> Scan_for_performance_issues -> Your_license -> Optimize_my_PC"
Then click "Reboot now".
After reboot I see some stages of loading GrimeFighter ("prepare to sleep", "waiting for a team", etc). Each stage is slow (5+ minutes).
Finally, I was connected to my Wi-Fi network (no problem there) and log-in to my avast account.
I was warned, that I have no GrimeFighter license. OK, I can't really RUN GrimeFighter.
But I can use it's browser (iceweasel). I type this text in that browser.
Also I got 5 karma points for using GrimeFighter.
Avast 2015 - the best
antivirus software game
Fixed in version 10.3.2223 (GrimeFighter -> Cleanup)