I'll have a look at how to simplify your scenes to avoid the Ah Snap errors. I think that some of the meshes you imported, such as the fireplace, are fairly high polygon count meshes. This appears to be the reason your browser is crashing.
If you are going to merge one into the other, I'd suggest maybe cloning the source file and then deleting all the pieces you do not need in the merge. I'd also suggest cloning the destination and deleting all the pieces that will be merged in from the other scene. Then do the merge between these two clones. This will ensure the result isn't larger than your current scene. And also if something goes wrong, you will have the originals around.