Debating downgrading from full to half marathon

For background, I’m (23F) relatively new to running—have only been running for about 3 years now. This past spring, I completed my first half marathon after 14 weeks of training. Training itself went pretty well, felt confident in my fitness level throughout. However, a month out from the half, I got a hip and foot injury. Went to PT and got it mostly resolved with additional strength exercises + switched shoes. On actual race day, my foot pain came back and I ended up having to run/walk the last 10K with a lot of pain. I decided to take about 2 months off from running to fully resolve my injuries and focus on strength training.

Last year, before I started my half marathon training, I signed up for a full marathon that will take place January 2026. I started training for it at the start of September and am now about 5 weeks in. There’s a 6 hour cut off time, but I’m starting to think that will be a struggle. I feel like my fitness level has dropped since this Spring. I’ve only had a handful of runs so far that I’ve felt really good about. The majority of runs feel pretty sluggish and like I can’t catch my breath. And so, my paces have slowed and my weekly mileage (14-16 miles) is lower than what it probably should be. I did just move from the Northeast to Texas so maybe it’s the weather? But can that really make my paces 2-3 mins slower than I used to be able to do? I’m just not sure if I’m thinking about this too prematurely. I have the option to downgrade my race to the half marathon, but if I do this, I feel like I’m giving up. Would appreciate any guidance on this—am I being overly ambitious? Should I reevaluate my goals?

TLDR: Now 5 weeks into marathon training. Feel like my fitness level has decreased since Spring half marathon. Not sure if I should downgrade my full marathon (January 2026) to the half.