Final answer:
Jessica can seek to deduct the full $28,000 interest expense for 2015 as it is the sum of the interest paid on the first and second loans, assuming her usage of the second loan for substantial home improvements allows full deduction under IRS rules.
Step-by-step explanation:
Jessica may deduct the interest expenses on her home as itemized deductions under the Internal Revenue Code. This includes interest on the primary loan and the secondary loan if the proceeds were used for substantial improvements to the home. Since she paid $18,000 in interest on the first loan and $10,000 on the second loan in 2015, she would be looking to deduct a total of $28,000. The limitation on mortgage interest deduction for tax purposes applies to loan amounts above $1 million (or $500,000 if married filing separately) when it comes to acquisition debt, which is defined as debt incurred in acquiring, constructing, or substantially improving a qualified residence of the taxpayer. However, we would need to consult current IRS rules and any applicable limitations to determine the exact amount that Jessica can deduct, given that tax laws change and there might be specific limitations depending on the total amount of the loans, how the proceeds were used, and the value of the home.