7dbi High Gain cctv yagi antenna vs 16 dbi high gain wifi yagi antenna

What is the better antenna to use if I am using a 2.4 ghz 4 watt a/v wireless transmitter and reciever for video transmission over an open field 1500m apart

Higher the antenna gain, better is the communication link.
1.5km is lot of distance for a 2.4GHz video communication, so the 16dB gain antenna would be a better choice.