Terrible VO2Max, any suggestions?

[Alex-db]

Started today; decided to do 30 mins on a treadmill, as far as I could without making myself too uncomfortable.

A mixture of walking at 7kph and jogging at 8kph and I covered about 3.75km.

Allowing myself to walk was a big deal, previously when I tried to start cardio I'd consider myself too useless if I didn't keep jogging, so I could never do a proper session.

I checked heart rate whenever I started walking and found I generally got uncomfortable jogging when it reached about 165, and I started jogging again when it was down to 145. I think I have read that that is a reasonable range to exercise in.

Plan now is to work my way up to doing 4k at a continuous 8kph, then to gradually up the speed for the whole thing until running 30 mins at a proper pace. (I don't like the idea of being on a treadmill any length of time approaching an hour, hence 30 mins but with increasing speed.