I’d love to lock in 30 years at a low rate, would free up lots of money for investment, but since that’s not an option I have to opt for clearing the mortgage i

I’d love to lock in 30 years at a low rate, would free up lots of money for investment, but since that’s not an option I have to opt for clearing the mortgage in ~6 years, and living like I work at McDonalds until that day arrives. Probably better for my long term financial health and peace of mind, but the opportunity cost sucks.