No rectilinear lens can 'replace' a fisheye, unless you always de-fish the images (in which case, you probably shouldn't have been using a fisheye lens).
The real question is how wide do you need? The 15mm fisheye actually gives a slightly wider FoV than the 14mm f/2.8L II. So if the fisheye gives you the FoV you need/want, the 14/2.8L II is likely your best bet.
The 16-35L II is a good lens, not stellar but a very useful ultrawide. It's a bit sharper than the 17-40L, but the 16-35's main advantage is the extra stop of light, and with a UWA you can often get the DoF you need if you're not right on top of your subject.
If you want the absolute best IQ in a wide or ultrawide, and/or if you shoot architecture/buildings, consider the TS-E 17L or TS-E 24L II. The TS lenses are also great for landscapes, giving you a deep DoF without the need to stop down so far that diffraction softens your image.