Have you timed them? I'm not saying I doubt you, but... that sounds impossible. I can't even imagine anyone being able to articulate what they're doing in that time, far or less decide and roll. Do they all speak at once?
No, they don't all speak at once. It's normally goes something like this.
They roll initiative.
DM - Mark, It's your turn.
Mark (moves the Wizard a few spaces) - I cast Hold Person on the Bandit there. (He rolls the dice).
DM (rolls some dice) - okay, Bandit cannot move. Jan, your turn.
Jan (Moves her War Cleric a few spaces to be next to one of the Bandits) - I attack this Bandit (rolls some dice).
DM - It's a hit, roll for damage.
Jan - Okay, (rolls for damage). I do 10 points of damage.
DM - Bandit is still alive. Bandit is upset. Gary, your go
Gary - Hey, I was going to hit this bandit, but since this one is still alive do you want me to attack the same one Jan did?
Rob - Sure, go ahead.
Gary (Moves his Fighter) - I attack the same Bandit (he Rolls some dice).
DM - You also hit the Bandit, roll for Damage.
Gary rolls some dice.
DM - Bandit is dead. 4 left.
Rob - I obviously am moving next as per what the dice showed. I am still concealed and I move behind this bandit here and try to stab them from the rear. (rolls some dice).
DM - sorry, it looks like you missed.
Rob grumbles in frustration.
DM puts down four different colors of D20 besides the still surviving bandits. This one attacks here, this one attacks Jan, this one attacks Gary, this one shoots at Mark. (Rolls the 4 d20, see which hit, calculates for damage at one we go).
That entire exchange doesn't take long normally,. Some fights last us less than 2 to 3 minutes real time. I tell the players how we want to run the game and combat normally and other situations and it just...flows.
I generally have more difficulty with some of my board game players (analysis paralysis at times) than from my RPG groups.
It normally just doesn't take a ton of time. Of course, if I DO get a player that takes overly long (not a normal thing, but I have had it on occasion) we will start a timer (since most of the players have gotten used to how we run combat, no one likes to sit around for a long time waiting for someone else to take their turn) which is an hourglass sand timer which takes about 60 seconds. Anyone can use it if they feel someone is taking too long.
The longest I think I may have could be a new player if we are playing in a mid to high level game and they are a spellcaster and are unfamiliar with spells. Others are normally MORE than happy to help them decide in those instances though.