So, your body utilizes fats and carbohydrates on an inverse curve depending on your HR or % of VO2 Max. For an example of what I mean check out the graph on this
LINK. The lower your HR, the more predominately you burn fat, as you approach 66%(ish) of VO2 Max you’re burning about equal parts fat/carbs(in the form of glycogen), and above that your body will predominantly utilize carbs(glycogen). I would guess that if you’re in the 150-160 bpm range you’re sitting right about that 50/50 point but probably still a bit under and burning more fat. Best was to find out where your HR zones are would be to do a Max HR/Threshold test. I’d recommend
THIS FIELD TEST then plug your average HR into
THIS CALCULATOR.
Once you have those numbers then monitor your HR during cardio and keep it in Z1/Z2. You’ll be burning predominantly fat and saving valuable energy for when you need it most, such as higher intensity lifting and interval type work. You’ll also find that over time with consistency, your HR will start coming down during cardio and you’ll be able to add more speed or more incline.
I know that’s a lot of info, let me know if you need clarification on anything. Hopefully it helps.