In 2005, i compiled linux kernel in 15 minutes on AMD Duron 700. Is true that was a very optimized kernel for my architecture, but i think that the typical kernel with all modules could get 1 hour or something.

Damn, thats pretty fast. Maybe I was doing something wrong in the config step?

not sure how much can really be done wrong, worst case would probably be an allyesconfig, which is huge, and while it was still big in 2010, it was considerably less so than now

I cannot overstate how poor the performance of various P4s was at the time.

Especially if you had some crap P4 that made modern gaming laptops look well-circulated.