The detail that changes this for me is the unresolved 150 m² figure. If it refers to floor area rather than the land parcel, dividing S$1,776,000 by it produces S$11,840 per square metre but says very little about whether the home is fairly priced.
Before leaning on that calculation, confirm tenure and both area measurements, then compare layout, condition, parking, outdoor space, micro-location and any shared charges with the completed sale. Ask the appraiser which differences materially affect the result. Until those points are settled, the larger risk is not choosing the wrong adjustment rate; it is building the valuation around unlike properties.