People talked about the framerate in LoS1 too, and I REALLy didn't notice it too much, if at all. And that's on the 360. I would occasionally notice some slowdown, but nothing game breakingly bad. I just chugged along without any real worries.
Now it's possible that also having the 3D deal, and being tiny card based rather than disc/Bluray based, it will have slowdown, since according to Cox, it was developed in HD first, then scaled down for the 3DS. (weird if you ask me, but maybe they were considering releasing the HD version at some point from the start.)
But some people don't seem to be noticing it that much...