Is it easy to fully decompile python compiled(*.pyc) files?

Depends on your definition of "fully" (in "fully decompile")...;-). You won't easily get back the original Python source -- but getting the bytecode is easy, and standard library module dis exists exactly to make bytecode easily readable (though it's still bytecode, not full Python source code;-).

Compiling .pyc does not secure the code. They are easily read. See How do I protect Python code?