Buying as a gift for my father whose feet are size 15. i know the socks say 13-15, but is it a comfortable fit for size 15? or does it run tight?

My husband is a big man with very "fat" legs and feet. He says they are very comfortable. He wears 13-15 socks.

How well do these hold up to physically demanding outdoor jobs?

I purchased them for my freshman college student. He walked or rode his bike to and from class, neither of which was a demanding outdoor job. I'm sorry this does not answer your question.

How well do these hold up to physically demanding outdoor jobs?

Hi! I bought these for my husband. Although they are very warm, he has big calves, they come up if you pull them up, a little below his knee. They do not stay up very good. Check out target for knee high or crew socks I think they are called 06, or 09's. then come back to Amazon and compare the prices. Normally Amazon beats them. Hope this helps!