Like most cars, you will get good ones and bad ones. If the car has been cared for, it would most likely be more reliable. There isn't any real reliability problems with the 155. There doesn't seem to be many posts about not starting/breaking down etc. Just remember that it is an old car now and may need bits replaced through wear and tear.
Just as a guide, I have owned my 1994 1.8 8valve for about 18 months.
In this time I've replaced: Tyres, front discs and pads (the discs were upgraded that's all), thermostat, drop link, plugs and leads and exhaust. The car has never failed me...Yet.
I would imagine the V6 would be a stronger engine as it may not have been pushed as hard as my weedy mota. Check the last time the belts were changed etc.