the end of every long run is just HARD, no matter what I do?

I’m training for my second marathon and I’ve literally never negative split a long run. I always start conservatively because I want to have enough left for the end, but once I get to around 15+ miles, it just gets really, really tough. I usually finish and (knock on wood) have not failed a long run yet, but I’m definitely not speeding up lol

I feel like I fuel pretty well….carb loading. gels every 3 miles, liquid carbs/electrolytes and salt tabs too. I don’t feel like I’m bonking because I didn’t fuel. It’s more like my legs just get SO tired and the thought of picking up the pace at mile 16+ sounds insane.

Today I did 19 miles and the last 6 were a real struggle. I finished, but I was basically just trying to maintain and get it done.

I guess I’m wondering if this is normal? Am I doomed to be a slow runner forever and never negative split 😭