If a typical combat takes more than 20 minutes, I have to ask "Where is the time going?". If it's the DM or players giving good descriptions of their actions, that's fine, but...
Idle banter: Not a problem of the system, maybe not even a problem if the group enjoys chit-chat.
Always looking up character data: Do your homework. Read the damned book.
Always looking up rules: This may be an issue of a player not reading enough, but it may be a sign the character or system is too complex.
Lots of rolls: This is probably a system problem. Look for shortcuts like rolling attack and damage at the same time when feasable.
Rules arguments: The DM is final arbiter of the game. The DM needs to do their homework. If a player wants to contend a rule is “stupid”, then the player needs to bring subject up before that rules is acting against the PC.