There's a topic (or eight) on this in the UK section of the forum...
Short answer... The dual 15's are lighter than the lvl 80 triple 16's, but do not add any range advantage and do less damage. So only use the 15's if you want to run with heavy armor and/or AA guns.
The other option is the quad 14" N guns of blockshotty goodness. They're devastating, but you will lack range and speed as they will max out your displacement with no room for armor.
So the most popular config remains the lvl 80 16" triples with no T slots and minimal armor.
