Happy that you found the Karvonen method first of all. The intensity is just the percentage of the zones. So zone 2 the lower end would be 0.6 and the upper intensity of the zone would be 0.7.

I'm using (0.5, 0.6), => Zone 1 (0.6, 0.7), => Zone 2 (0.7, 0.8), => Zone 3 (0.8, 0.9), => Zone 4 (0.9, 1.5) => Zone 5

If you are able to reach 215 the problem might be that most of the calculations do 220 - age or something similar for max heart rate.