Paris - Charles De Gaulle Passport Control and TGV Train

If your flight is on time, 2.5 hours should be plenty of time. Just don't linger.

The rule of thumb is 3 hours. Our plane was nearly an hour early this past week; in past years we have almost always been late, once by 5 hours. Passport control was well staffed and we spent only about 10 minutes there (about 10 to actually get there, so 20 minutes). Our luggage was up immediately but we had traveled business class and it gets offloaded first. In past years in coach it has taken about an hour on average; people here have reported it taking two hours. If the plane is on time and passport control is well staffed and three huge planes don't unload right in front of yours, you should be okay, but it is tight enough that if anything goes sideways you could miss the train.

What airline? United lands at Terminal 1 and you have to take the CDGval shuttle train over to Terminal 2 where the TGV station is. That can take 15 to 20 minutes.

We are arriving on Delta.

Not sure there is enough Tums and Maalox in the world for me to try that.

As already noted, your 'fudge' factor is paper thin.

Good luck and may all go well

You'll probably be fine, but as a change why not consider packing light with only carry-on baggage to avoid the wait for baggage and speed up your connection.

Don't fool yourself: you can do it. Before we moved here my wife and I spent six weeks in France and the UK, traveling from the U.S., with only carry on luggage. The only thing stopping you is stubbornness and an absolute conviction that what is possible is not possible.

We've been in France for years now. You don't need huge bags. No one cares about your clothes. Pack light. Carry your belongings. The freedom is liberating.

I've already done this sort of connection lots of times - from plane to train and plane to plane. I assume the OP knows there's a risk of delay - I always know it and take the risk. I didn't speculate on what the risk factor might be - only that if the flight lands on time, 2.5 hours should be plenty of time. (And yes, I have done a connection at CDG to a TGV train.)

CDG Information Site: http://easycdg.com. Help you get the lay of the land. Delta lands in Terminal 2E according to the CDG site, so you are in luck in being closer to the train station.
Enjoy your trip.

This site gives you good directions for getting to the TGV station in CDG.
https://parisbytrain.com/paris-airport-terminal-2-train-photo-tour/#arrival