The phrase "to decrease the interest" means to reduce or lower the level of attention, curiosity, or concern someone has towards something. Full definition
Unfortunately, the government can't just «fix» this issue by decreasing interest rates since its borrowing costs will still remain the same. (studentloans.net)
A brisk morning workout decreases interest in food, as measured by brain wave activity, and doesn't make subjects eat more, according to new research. (health.com)
However, in many cases, it is not, and only gets people to stay in debt for longer by decreasing the interest and minimum payment while the loan amount stays the same. (financialwellness.org)