User blog comment:Hayashi H/Advanced Equipment Guide/@comment-114.125.12.189-20151105060725/@comment-26486243-20151111143855

Just an update. Qunow and I did a check yesterday regarding the claim of a Twitter post that 15.5cm triples have a fit bonus, and found no such information. Nor did we find any information regarding the exact guns that have fit bonuses, only a nebulous 'smaller guns have an especially large bonus when multiple smaller-calibre guns are equipped.'

In other words, there is no official statement of 15.5cm triple guns having any sort of bonus specifically. This does not necessarily mean it does not have one - it does, however, mean that the only substantiation available will be stat tests conducted by players.