If you're running 8min miles in zone 2 then you can probably just ignore my advice. What's giving you your heart rate figures? Zone 2 is my goal for "easy" runs. I also struggle to run slow though and most of the time that ends up in zone 3 instead. Going slower is definitely harder than running fast IMO and I really struggle to not look at pace when attempting to do so. From what I've read, your heart rates zones are the easiest way to adjust your running for slow, tempo, 5k, whatever run you want to do. Since everyone runs at different paces.