It's already doing great and can only go up. As far as non-GOT related Universe shows go, TLOU already is less than 1 million viewers behind the all-time HBO record set by Euphoria last year with 6.6 million viewers in the finale episode of that season. TLOU, if it keeps increasing, looks to surpass the 6.6M Euphoria saw last year fairly easily (that's Sunday night viewers counted only) at some point in this first season of the show.
With an audience so large, it really does make me wonder what they'll do for a season 2. I just can't see them diving right into Part 2 for various reasons (or at least not the whole second game), but if they are to tell an in-between story, it has to be worthwhile and not just to pad seasons since the show is bringing in a sizable audience. If you do a tweener story and it has the same level of writing and care that they've given to the added parts or changed up scenes.