What type of loss? Is this a passive loss, capital loss, business loss (which would be unlikely)?
Are you using TurboTax Business to prepare a Form 1041 for the trust?
More details are needed as your question is overly broad.
Q. Can we deduct a $10,000 loss against $15,000 of dividends ?
A. Simple answer: no.
A capital loss can only be deducted DIRECTLY against capital gains, including capital gains distributions (box 2a on a 1099-DIV).
Only $3000 of Capital losses may be deducted against ordinary income, including dividends (including "qualified" dividends). Any excess (over $3000) is carried forward to the next year. Although qualified dividends are taxed at long term capital gains rates, they can not be deducted directly against capital losses.
Note that if the $10,000 loss is a capital loss, you are distributing all of the ($15,000) dividend income to the beneficiary(ies), and this is not the final year of the trust, then then entire $10,000 loss will be carried forward to the trust's next tax year.