I have both, although my 815 isn't really under the "Trumpeter" name. (I bought it a few years back...)
The Trumpeter is wired for a motor, to run the model, and the plastic seems to be of different quaility than the Tamiya. Both overall, it's the same model as far as I can tell.
I also have the Trumpeter Vosper (but not the Tamiya)...I'm assuming it's pretty similar to the Tamiya Vosper...
Sam
Quidquid latine dictum sit, altum sonatur :)