At one of the companies I worked with when I was doing consulting, they could make the slow tests, which used to take around 3 hours, run much faster and in parallel by throwing engineering and hardware resources at the problem. First it was 30 minutes, then it was 10, then around 2-3 minutes.

I think it was one of the best investments that company made.

So my point is, don't delete slow tests, just make them fast.