As said many times, the bank is probably screwing you on the FX rates.
Also there are loads of studies that show you are better off investing in a low cost diversified portfolio than paying off your mortgage quickly, esp at rates of 2 to 3 %.
That being said I am considering overpaying on my mortgage slightly , esp with a possible rate increase that may happen during the course of this year.
pin you know I am leveraging, meaning that with the low interest rate loans I am borrowing I am doing some investing in HK, AND at the same time also paying off my overseas mortgage. So I do try to diversify myself and not just doing one thing.
Also regarding the bank screwing me on fx rates, are you referring to the JPY loan I have at 1% interest rate? In this case, I simply use standard chartered online banking to transfer as much or as little of my loan as I want from HKD to JPY. When I do this, I get the usual bank rates, which of course yes they take their cut via the gap between TTB and TTS rates. But this is not something they keep taking a cut of every every month or something that is hidden. For example, if I transfer HK$80k to around JPY1m, then sure the bank gets their usual cut of this transfer, but then each month after this they are charging me interest in JPY around JPY800 (1%). Its all in JPY with nothing hidden going on. If I had left the money in HK$80k, then each month I would be charged interest around HK$116 (1.75%). So sure plenty of fx vs interest rate risks and opportunities available here, (and actually the JPY I transferred about a month ago I could make a profit by transferring back to HKD today but choose to keep it in JPY due to lower rate 1.75% vs 1%), but I don't think there is any actually screwing going on here. The bank only takes their usual cut once off when doing a conversion and nothing hidden in between.