The 1.6 TDCI is a PSA (Peugeot Citroen, now Stellantis) engine. It does not have the greatest reputation, but that may be slightly unfair. Doing some research for a potential van purchase some years ago, what I found is that the engine is actually very reliable providing a couple of key points has been adhered to. First, when the engine first appeared (not sure about later ones) I believe the service intervals were about 20k miles, which seems to have been too long. Second, it is apparently critical that the correct grade and type of engine oil has been used. The first those is easy enough to look into, but how would you determine that the correct oil has been used on a second hand car, especially if the car has been serviced outwith the dealer network?.

Not sure if the 2.0 is also a PSA unit, but it does seem to have a better reputation than the 1.6.

The 1.5 is just a smaller, updated version of the 1.6 and as such should certainly have the potential to be reliable. But I have not looked into it, so not sure about any specific issues.