An upgrade might work, but not get what you want.
My observations as a wattOS end-user (as opposed to developer), are that :
- historically, wattOS has had less and lighter applications than mainstream Ubuntu, and has been carefully stripped-down of the "luxury extras". (And sometimes that has meant users have needed to find a driver which might have been included in U.) So there's quite a lot of config work in there from Biff. I recall that this started from the U "alternative install iso" as a base.
- recently, Canonical have also released a "core" version of U; I get the impression that using this as a base results in more building-up rather than stripping-down, but again omitting larger and heavier material.
- not least has been the integrated use of LXDE in wattOS in lieu of than Gnome/Unity.
If I've observed correctly, then an update might work (and might not), but even if it did you could find that there is a large amount of material and different configs which mean that what results is not really wattOS.
Lubuntu is in a different position, being an official U variant. Users would need to be able to upgrade, as a matter of course.
(I agree with Leenie - 4 hours seems a long time for an in-place upgrade.)
If you have a clone backup of your wattOS (and hence a complete recovery option) then you could try the upgrade an see what you get. I'd suggest first searching online for experiences of upgrading U from 14.04 to 16.04, so any major pitfalls can be avoided, but it would be an interesting adventure, no ? :-)