If you don't fancy the whole landlord thing, then I think you have just answered your own question. Why have an asset earning you nothing when it could be saving you lots of money on reduced or eliminated mortgage repayments. With interest rates getting higher than we have all been used to recently, I think selling is the best option for you.
Incidentally, you mentioned that the house is in the country - did your agent say how quickly they expected the property to move? Just bear in mind, that it could take a few months to shift it (then again, could sell immediately). Check out if there were any properties for sale in the area in the last few months, and you should be able to gauge how quickly their shifting
Best of luck - yours is a nice position to be in!