Assuming your BA flight is on schedule that is plenty of time. The gates the BA flights use exit pretty much directly into the passport hall, then it will take you about 15 minutes to walk to the TGV station at a leisurely pace. I would say if you are HBO the BA flight could even be an hour late and you would still make the train if you run. Unrelated, but remember that TGVs from CDG to Lille go to Lille Europe station not Flandres, on the other side of the shopping centre.