Too shallow, it will crack. Fact is the pipework should not be in direct contact with plaster.
It can run behind plaster board but stucking it in render will create all sorts of issues. Firstly it will crack and it could also attack the copper, what happens
if you get a leak or you hit it hanging a picture. Repair could be a night mare.
Think of future maintenance and hiding pipework looks great now but in 5 years when a leak starts what then. It's bad enough taking up floor boards and a plumber will charge you a big premium for finding a leak in a
wall and he won't guarantee his work from future leaks. Plus your insurance might not pay out