Is there a way to calculate the approximate amount scholarships will get taxed?

I had a scholarship for $23K, $8K which was used for tuition fees/expenses, leaving me $15K that was mine. I actually used it to pay off college loans. How much taxes do you think I will have to pay?

A scholarship recipient may exclude from gross income the amount used for tuition and related expenses (fees, books, supplies, and equipment required for courses), provided the conditions of the grant do not require that the funds be used for other purposes. Amounts received for room and board are not excludible and are treated as earned income for purposes of calculating the standard deduction for a taxpayer who is another taxpayer's dependent.

Call the Internal Revenue Service at 1-800-829-1040