However, looking at the numbers, if you're looking at buying 1500 Crowns to access this DLC and you're not wanting to spend more to buy a larger pack, your best bet is to buy a one month ESO Plus Membership
and then cancel it so it doesn't renew automatically. Hear me out...
A one month ESO Plus Membership is $14.99 USD, the same price as simply buying 1500 Crowns, but you'll have access to the Horns of the Reach DLC for a month - without spending the Crowns on it - and you'll still get 1500 Crowns, since that's the Crown allotment that comes with a 1 Month ESO Plus Membership.
Then... if you find that you really like Horns of the Reach, you can use those Crowns to purchase the DLC after your membership has expired. If you don't like Horns of the Reach (or you are done with it and don't want to return after the month of access) then you can spend your 1500 Crowns on something else. And, finally, if you find that you do like the ESO Plus Membership, you can either turn auto-renew back on and buy it month-to-month, or opt for the longer-term memberships to pay less per month, keeping the 1500 Crowns to spend on something else, entirely. Note that all of the ESO Plus Memberships come with a Crowns allotment. If you haven't looked them over, check them out. Yes, they're subscriptions, but if you're going to be buying Crowns, anyway, they might just be the best way to go.
I'm not trying to push them or anything... just thought it was worth pointing out that it basically can equate to a one month trial period not only for a given DLC (such as Horns of the Reach, in this example), but to all of the other DLC... and you still have the 1500 Crowns you were going to pay for, anyway.