Which length Ally?

Hello everyone, after much research I've decided to replace my old 16ft Venture Prospector with an Ally foldable, a DR model. This is mainly because the folding aspect would be a great benefit to me for storage and transport, also I've been watching every programme Lars Monsen has made on NRK.tv which has demonstrated just how good these canoes are. The question is though, whether to get a 15 DR or a 16.5 DR. About 70% of my paddling is solo and with a light load, day tripping with a small bag, dog and fishing gear. There will be times however when there's 2 of us, 2 largish 100 litre bags and the dog, on water such as Scottish rivers, Lochs and Estuaries. I've never had a problem paddling my 16ft venture solo, although it is rather heavy off the water. I've done much research and have found that 15 DR's are popular for solo, but can't find much about using them tandem with a load and vice versa I can't find much about soloing a 16.5 DR. Mr Monsen seems to use both sizes in his films but mainly a 15, although that's always solo.
Has anyone got some experience of either paddling a 15 DR tandem with a decent load or alternatively a 16.5 DR solo unloaded, (I could always use water bags as ballast). I would prefer the 16.5 but only if it were manageable solo. Of course the obvious answer is to get both, but neither funds or the wife will allow that! Many thanks in advance, Nick.