I live on a usable late model boat in HK. The boat is spacious and has more mod cons than an apartment. Pull out and anti-foul costs HKD 24000 per year, insurance is HKD 25000 per year. The other costs vary from marina to marina and DB debentures and live aboard fees vary as well. 15 Mill will get you a very nice 2400 square ft floating trailer in DB and leave you with a fair chunk of change, if you want a usable boat it will get you less space but a lot more boat.
PS, I use my boat on a weekly basis and in two years have not even begun to explore all the islands and beaches!!