Edit: CORRECTION! Sorry I didn't look far enough... the 2.0TS 156 sump is used on the 1.6 16V 155, but for some reason the 1.8 16v & 2.0 16v use different sumps.
(all the 156 TS 16v sumps are the same)
I suspect the only difference is that the bigger 155s have a couple of extra tappings in the sump for oil level and temperature sensors, not shared by 145/6, 156, or GTV. So if you use a sump of any of the latter it'll fit but you'll have a couple of dangling wires and the level indicator and temp gauge won't work! Then again many people say the temp gauge rarely works anyway