Ask HN: Optimal webpage weight?

Would anybody be able to point to resources describing in details the attributes of an optimal webpage (or at least pointers)?

I understand "optimal" is subjective, however I have heard over the years that 15kb or less is an ideal size (gzipped or not?), that browsers theoretically only open 6 connections at one time to a single server (though Chrome doesn't seem to care much), that certain headers are redundant, etc.

I've never been able to confirm any of this and I think it's very interesting (if not nearly vital) to know. It seems HN itself abides more or less to the above principles, and I'm guessing this isn't just a coincidence.

Thank you for your help.