Heading to Spain in summer for guided holiday. They suggest 2ply tyres with tubeless set up. Any disadvantages in running my normal hr2 with a slime tube? Was going to tubeless them should the 2ply make that much difference?

I would suggest you’d be wasting your time with the slime tube, you put a pinch cut in it and it won’t seal! Minimum would be the two ply tyres and standard tubes or just set your wheels up ghetto tubeless with some 2ply rubber.
You will hate yourself if you ruin your trip by not heeding their advice.

HR2 will be fine tubeless, double the stans.puncture free IMHO