i assume that the 5.65% is fixed for e.g. 25 year mortgage, 5 years fixed and 2 years in have 3 left on fixed and total of 23, and you want to reduce it to 15 years. Most likely you will only be able to do that after the end of the fixed period. Otherwise you would require to break the fixed rate and pay a break cost. Given that you are reducing the term and making extra payments it is possible that the bank may do a deal with you if e.g. the remaining term after fixed period of e.g. 20 years is ECB tracking then the bank may do a deal with you if it is to go to variable, or indeed still ECB as the bank will have less duration to fund. It's always worth a try, but I wouldn't hold my breath.