Can I just lay new tile over existing in bathroom without tearing up?

No you need to tear the old tile up and check to see that the sub floor does not need to be replaced. If it's okay then you need to scrape off all residue extremely well before layinh new tile

Chris, you CAN lay new tile over existing tile (I am assuming you are talking about CERAMIC tile, AND that you have a solid floor, concrete, uncracked floor, although perhaps I shouldn't do that). You will have to do some prep work first, like sanding down any high spots (find those by using a 4 foot level on the floor), and then sanding (with 80 grit sanding belt), and cleaning off the dust, etc., so the floor is clean. I think the first thing you would want to do, though, is replace any loose old tiles because your new tiles will have to be attached to the old tiles and you want them to be solidly attached to the under-flooring). I am posting for you a website link that will tell you in detail what you need and how to go about this task. I hope it all goes well for you, and thanks for the question :)

https://www.familyhandyman.com/tiling/tile-installation/tile-installation-how-to-tile-over-existing-tile/view-all#step1

If your old ceramic tile is worn or dated, you can lay new tile right over the old, and avoid the huge job of tearing out the old tile. This assumes that the floor underneath is solid (concrete) and that there are no cracks in the existing tile (indicating underlying problems in the concrete).

No

Just be sure if you removed the toilet to do this job that you realize the new floor will make resetting the toilet trickier. You may need to extend the connection to the floor and a larger wax ring and longer bolts.

thank you everyone!!

I have read that tiling over tile is possible...if...the old tile is in good shape. You should do a dry run especially near the doorway to make sure it will not be too high. In addition, I would remove the toilet , tile and then use thicker wax ring to replace the tile. The toilet should sit on new tile...not be seated below new tile.

It will fail, the tile needs a sturdy surface and the grout (not plaster), will crumble and you will end up spending much more money than if you did it correctly the first time around.