How slow is too slow?

I’m a novice runner currently training for a marathon and I’m about 10 weeks into the training plan. It’s a standard training format with three shorter runs and a long run per week.

The problem is that regardless of the length of the run, the temperature outside, my level of rest/food/caffeination, or any other factors, my runs are too slow. The first mile might be a 12-14 minute pace and then all remaining miles are at an 18-19 minute pace. People regularly walk past me.

Now, despite conventional wisdom that would tell you that you WANT to do your training runs at a slow, conversational pace, this is objectively TOO slow, because my marathon has a 7 hour time limit, which means I need to somehow speed up to 16 minutes per mile. I expected this to happen naturally, but….

After 10 weeks of training, my pace has not sped up at all.

Now, I can certainly FORCE myself to move faster, for a few moments, by actively engaging my mind and speeding up. This works for a minute or so until my mind wanders back to my podcast and my body slips back into its comfortable 18-19 minute running pace. I can rinse and repeat, but I inevitably slow down as soon as I take my mind off of actively focusing on running fast.

Short of replacing my podcasts with a 7 hour loop of me chanting “run, fatty run!” I don’t know what I can do to improve my pace so that I actually can finish this marathon come race day.

I’m not overweight, I have no injuries, I get plenty of sleep, I know all the running tips (Lean forward! Lift your legs more! Move your arms!) but again, as soon as I take my mind off of actively thinking about running, I slip right back into my natural 18-19 minute pace.

Has anyone else dealt with this problem? How do I make my natural, subconscious pace faster? Will I magically speed up 2-3+ minutes per mile on race day with adrenaline?

Any advice is much appreciated.