Do slicks last longer than treaded tyres?

Yes, they do.

When track conditions are optimum, slicks will wear out slower than sticky treaded trackday tyres.

The treaded tyres get worked a bit harder on track but it’s not as noticable when track temperatures are lower. When track temperatures are higher, treaded tyre wear rate increases. Therefore the difference between slick and treaded tyres in terms of longevity on a sunny Spanish trackday is noticeably in favour of slick tyres.