For 2 adults wil it be cheaper to take a taxi from Hong Kong Airport to JPlus Hotel in Causeway Bay

If take a taxi from the airport to the hotel, it’s about HKD285.
If you take the Airport Express, you should get off at HK Station. The fare is HKD100 per adult. Then take a taxi to the hotel, about 4.4 km, and the taxi fare is about HKD30. So the airport express + taxi is a bit cheaper.

If you want a cheaper way, you can take the bus E11 from the airport and get off at Sugar Street, Yee Wo Street. Then you can reach your hotel within several mins walking. The bus fare is HKD 21 per adult.