This is a great question and this is an important topic. Let me give you an outline of a persuasive speech on the topic of decreasing federal school loan amounts.
First, since this is a controversial topic, you should put the people at ease by saying that you know that it is a controversial topic. This will let the people know that you know the issues at stake and more importantly you know they might feel.
Second, you should give some solid reasons that would help those who get a decrease in federal loans. You might want to mention the negative aspect of having debts. Think of where our economy is because of debt. Or you might want to let people know that higher education is not for everyone.
Third, you should give some alternatives and options. In other words, if people do not get loans, then what should they do? You might want to suggest working and going to school part-time or getting your work to pay for school, as some companies have this program.