At most - purchase EAP. Once you purchase EAP - you can subscribe to FSD for $100/month (or $200/month if you bypass EAP). When you look at this all from a financial standpoint, it makes zero sense to ever purchase FSD outright for many Tesla vehicle owners. 15k/200=75 months. If you purchase EAP, 9k/100=90 months. Chances are you won't keep the vehicle either 75 or 90 months. That's 6.25 years or 7.5 years. Chances are you'll trade your Tesla in for a newer model or move on to something else before those timelines come and go. And if you look at the opportunity cost of dropping 15k when you could invest that money over the same 6-7.5 year period - it makes even less sense.
Since FSD is tied to the vehicle - you cannot take it with you. So why pay up front for it? So, at most, if you see real value in EAP, buy it as part of the vehicle purchase for 6k, and then subscribe to FSD for $100/month. The FSD subscriptions can also be cancelled at any time for no additional cost, so you can subscribe/unsubscribe as needed on an ongoing basis - which drives the cost down even more over time.