Hm...are you looking at the right fare? It's because it is $7.7 for seniors or children.
http://www.citybus.com.hk/eng/RouSer...outenumber=182
http://www.kmb.com.hk/chinese.php?pa...om=&select_to=
Both KMB and CTB operate route 182 because it is a Central Cross-Harbour Tunnel line. Newer Western Cross-Harbour Tunnel lines and a few Eastern Cross-Harbour Tunnel lines are operated by one bus company.
One important thing about HK's buses is that the closer location you board a bus to the bus route's destination, the cheaper the fare will be.
Take 182 as an example, its final destination is Sheung Wan Macau Ferry. If you board the bus in Hung Hom going to Central, your fare will be only $8.9. However, if you board the bus in Wan Chai heading to Central, your fare will be only $5.4. In your case, you will be boarding the bus in Shatin, so your fare is $15.3.
Hope this helps~