Yup.

Actually, on the highway, a 1.5 liter engine of the same generation of technology as a similar 2.0 engine (carburator versus carburator, EFI versus EFI or direct ignition versus direct ignition) will drink less gas, as long as you drive it at economical revs.

But if you drive it expecting the same speed as with a 2.0, it'll suck gas like crazy, as it has to work harder to accelerate in the same manner.