If your client is going to have losses for 15 years he's probably not generating goodwill.

But yes you amortize it over 15 years.

Amortization reduces the basis in the goodwill.

If he sells the goodwill later, the difference between the sale price and the adjusted basis of the goodwill is a capital gain.

And amortization reduces ordinary income at regular tax rates while LTCG is taxed at a lower rate (at least for now).