The kitchen designer stated that the end panels for the fridge should be a minimum of an inch and a half. Vs 3/4. Is there a right or wrong answer.
No, not really. A 3/4" end panel is implying an edge banded piece of 3/4" panel, which yes, tends to make it a little flexible. The 1-1/2" would tend to imply a face frame, which would make that more stable, or rigid.
It may have something to do with your cabinet line. It may or may not come with what you are requesting. Euro cabinets are more likely to have the 3/4" panel only, but not always. Not sure if a face frame system would have a simple 3/4" panel though.