Not to mention that HK$15,000 will not get you far in HK. This is an entry level salary which usually relies on the individual being able to live at home with their family. Unless you have someone who you can live with very cheaply, you will not have a good quality of life at this level.
Just to give you some benchmark, the lowest paid person in my team earns HK$16,500 per month plus benefits such as private healthcare and up to three months bonus. This is for a junior secretary position. Admittedly we are a big MNC and therefore probably pay higher than average salary, but HK$15k for what sounds like a relatively skilled role sounds like someone trying to take advantage of someone who is from a low salary economy.
I suggest you explain to them that having looked into the cost of living and market rates, this salary is not enough for someone based in HK and either negotiate a rise or investigate whether it would be possible to do this role remotely from the Philippines where HK$15k would stretch much further.