It could be very quick if you do it the right way.
I'd proceed like this :
1) Find the exact last AGS version that had a working Android port (I don't follow the Android port too closely so I couldn't tell if it's an older version or the lastest version. Who knows, you might be lucky). For argument's sake, let's pretend it was AGS 3.3.0.
2) Convert your game from 2.x to 3.x using the 3.x version of AGS that had the best retrocompatibility and upgrade abilities with 2.72. If I recall it could be AGS 3.2.x but maybe someone else could shed some light on this topic.
3) Make sure your game works on that version. You might have to mostly work with converting from global function to object functions. (for example: GetColorFromRGB is now Game.GetColorFromRGB, ChangeRoom(cEgo) is now cEgo.ChangeRoom(), etc.)
4) Convert your game from that version to the version we mentionned in step one. For example, convert from 3.2 to 3.3.0 if these are the versions. This time your main challenge might be to convert to the new sound system (convert from "PlaySound(1)" to "aSound1.Play()")
Done!
EDIT : out of curiosity, what game was it? Is it in the games database?
