I can do many forms of exercising as long as I am not over-stimulated or over-attending. When I am at the Y, I do 20 minutes on the rower with foam ear plugs. If everybody around me has their ear buds in and listens to their own music, I do fine. When a chatterbox starts talking away, I have to cut the row short. If a heavy footed runner uses a nearby treadmill, the pounding sound causes me to cut short. I know that when the stimulation starts to be a focus rather than ambient sound, I need to leave.

I have the same problem in the pool. The aqua aerobics instructors like to turn the music up. Some music selections will cause me problems. The echos are the biggest problem.

You could try walking with ear plugs to see if your gait had a pounding foot plant. You will hear your foot plant. That can be a problem. Finding a softer gait and softer walking shoes can help.

I don't see a value to the longer walks. I think you would be better to have a broader range of activities. The idea of pushing for a longer period may not be as good as learning how to do a wide range activities and remain symptom free. The stress of "I'm going to finish 1 hr 15 mins" may not be helpful. Just do it with a a specific target.