As long as it's all on one ticket (and at Lille Europe, as stut said), then it should be fine. Lille Europe is a fairly compact station, and they should be somewhat flexible with the check-in time - and may even hold the Eurostar for a few minutes if there's a backlog at security. However, most importantly, as long as it's all one ticket, even if the TGV is late and you miss the Eurostar entirely, they have to rebook you on the next one.