First congrats and keep going. You're a leg ... or 3 maybe! ...up on the vast majority of the 19k candidates in your class pool.
Still, as has been well noted on this and other forums over the admission seasons, there are a surprising number of LOAs who do not receive nominations nor, obviously and consequently, appointments.
Further, I'm not aware of any LOA recipient who has ever received a NAPS or foundation slot. So, assume that is no longer a potential option for you.
So those are the "bad" news, and of course, worst case scenarios and not what the vast majority of LOA recipients come to realize.
The "good" news? Your upside is terrific and you have now, a fair advantage on your fellow candidates.
Now, one thought. I'm afraid I'd sorely disagree with osdad's always good counsel in this case. Failing to somehow acknowledge and inform (NEVER assume the interviewers are aware.) is not what I'd advise. True, they probably are fully aware, and the better scenario would be to allow your interviewer(s) to acknowledge their awareness of your status as an LOA recipient. But failing to ensure that is the case would be both disingenuous and risk being perceived as less than an LOA recipient should be. It's a critially important aspect of your candidate profile, important to the mission of your interviewers and needs to be fully known, imo.
So not to beat this point, and most certainly HOW you might make sure that it is understood could reflect upon your candidacy in either a positive way or less than that. So I'd consider this as you prepare.
In sum, if it's not brought up, I'd not want to risk walking out of that interview wondering if they were informed of your special status awarded by the Academy. I'm unaware that keeping this information under wraps is "usual advice." Just my thoughts. This is not the moment for false humility nor being ill prepared to put forth your best possible image in the best possible light. Shine and knock 'em dead!
And don't allow having that LOA delude you into thinking these personal opportunities call for anything less than doing your best.