This makes no sense to me... whatever your interest rates are, that is the amount you are being charged at to borrow the money. Regardless how much you are paying back. It's not like they have frozen the interest they are charging you.
if you are struggling for cash, I can understand dropping the amount..
Unless this is your final mortgage... if you're not already on a higher rate, the amount you owe at the moment will be charged at the higher rate when you renew it.
Even if this is your final mortgage, I personally would perfer to pay it off as quick as possible and then maybe a few very low ones so I don't get fine for ending the contract sooner, so I can use the money when it is paid off to go on holiday.. lol