Personally, I wouldn't bother. It was a fantastic game, and it has been remastered I believe, but for me it feels quite dated. Also, two other things to consider.
One, the hype is going to be insane when it's released - do you have the discipline to start the original and not play the new one if everyone and their mother is talking about it being, likely, quite amazing? (I'm only half through AC Odyssey and I just know I'm not going to finish because of RDR2 lol)
And two, RDR2 is actually a prequel to the first, so you could play the new one and then continue the story with the original if you feel so inclined.