Even if it’s not, houses appreciate 5% a year on average. Assuming average appreciation over 10 years that house is now worth ~163% of its original value. That means that the mortgage was taken out for ~61% of what a comparable house would go for today which assuming the same interest rate would be a fairly significant reduction in the monthly payment. You also have the potential to refinance to further reduce that monthly payment.
Or you could sell it and get that 10 years of equity + appreciation out in cash and that might be enough for a sizable down payment elsewhere.
TL;DR unless your parent’s place is a dump in a low demand area it’s an asset even if it isn’t paid off.