Am I wasting my time here in this zone?

I am training for a HM in april with target 1h:45 finish time and a sub 4 marathon in September. I live in places that have heavy snow, therefore tempo, threshold, and intervals are limited to how well the roads are cleared of snow.

It has been snowing heavily, so I have skipped everything and focus on zone 2 training.

I spent almost 2 hours running at 7:41min per km (12:23m per mile) at hr 135bpm which is slightly above my garmin zone 2. During the run, i can easily have a conversation if I had someone to talk to. 20 minutes Before my run, I had a bagel with jam and oatmeal. I spent 2 hours running with a candy at 60 minutes mark. After the run, i felt great and I can easy do more if I refuel with something.

My question is am I wasting my time here at z3? Should I slow down and be in z2 or this is fine and I should keep it up?

For instance, my DSW to build my base for at 5:40-5:55, but I would be running at zone 3 or zone 4 with hr 150ish.