I'd like to see them open Photoshop or something chunky. That's what I recall taking much longer on my G3 Macs than it does on my M1 Pro Macbook.
They should probably run some sort of antivirus too; this is built-in for Windows now, ya? That'd be my first guess for the small programs. My memory of those days doesn't feel any faster than today, but I never had anything as top-of-the-line as a 600Mhz chip in 1999, more like half of that.