Don't think of it as a debt. It is not a debt in the normal sense of a loan / credit card / mortgage etc. as you only pay back when you are earning above a threshold, and the amount you pay only depends on how much you earn, not what you 'owe'. The amount of the loan is pretty meaningless.
Think of it along the lines that the government has paid for your university education, and when you are earning you are paying an additional tax to reflect this. As mentioned elsewhere on the thread, any outstanding 'loan' is written off after 30 years. Unless you've been fortunate to succesful enough to earn a significant salary though out your career and therefore pay it all off. In that case you've probably done alright for yourself!