Any experiences with a longer taper?

[u/Sad_Pomegranate_1331]

How have people navigated peak week while managing injury? So far, my longest long run was 19 miles during week 13 of training. I'm in week 15 right now with a 20-mile run slated for Sunday, and I'm not sure if I should just try it, adjust the distance, or cross-train instead. For context, I run my long runs at an 11-minute pace, so a 20-mile run will take around 3 hours and 40 minutes. What would a longer taper look like if I adjust now?

For context, my ankle mobility has always been poor, and the rest of my leg has taken the brunt of it throughout the training cycle. Most weeks it feels completely fine, but I took a week off midway through training due to arch pain stemming from ankle issues. Recently, things have been feeling alright, and I completed 19 miles pain free and feeling really great. I had an intense 8-mile speed session on Friday that I think I overdid in terms of pace, with some hills and heavy impact on declines, when most of my runs have been easy throughout my training block. I noticed my shin starting to feel tight and uncomfortable at rest over the weekend, so I skipped my 12-mile long run on Sunday (technically a deload week). Today felt fine, and I did a 2-mile easy run, but everything was tight in the lower third of my leg toward the end of the run and still is now. I know it is likely due to my poor ankle mobility (I'll confirm with my PT this week), so I don't believe it's anything structural that would stop me from running the race in 3.5 weeks.