I added a 2.2kw spindle (just to the stock Z-axis) and was a bit concerned about the extra weight so I made a bracket to hold stronger / longer springs (longer to get a bit more of a constant-ish) force.
Here is a link to some pics in a post I did at the time:
I don’t know what the weight of a 1.5kw unit is - but if it’s not substantially more than your stock standard Dewalt/Makita unit I probably wouldn’t worry about it too much.