If it doesn't involve any wet works, 15k is possible.
But you will need to do alot of DIY shopping via taobao and shopee for items such as down light, track light, sofa, TV cabinet, dining table, etc.
Since your unit is 800sqft only, I presume only 2 rooms?
Just hunt for the cheap bedroom set.

Ranging from rm1k to 2k, can get 5ft cabinet, queen bed, makeup table, side table.
Mattress you may want to invest a slightly good quality ones, might cost 1k.

Aircond you can get Midea 1hp for about rm800 installation rm200 back to back or rm18 per feet if need extension.