Is the account your own personal account? Will the buyer be granted access to the e-mail linked with the Minecraft account?
You can purchase a list of 5,000+ Minecraft premium accounts for $7.99 - or even purchase a single Minecraft premium account for $0.30¢ - therefore I see no reason as to why you're selling a premium Minecraft account for $15.00.
It is my own personal account. The buyer will be granted access to the email linked with the account. I have the list of 5,000 and I tried around 300 of them to no avail. This account has multiple offline huge builds such as a spaceship and a cathedral.
There is multiple different lists, you most likely have a list that was obtained through a giveaway of some-sort.
Off-line builds don't matter as the world(s) will only save to your computer; once the buyer has logged in-to his own computer using your account details, there will be no single-player worlds.