Again, how?
Presume a Very Hard encounter, for your group of 5 players (7th level PC's) that have played their PCs from 1st to 7th and are familiar with their characters abilities.
You: As you walk out of the forest, the (CR10 monster) attacks. It's 60' away, 40' up and swooping down from the air. Roll initiative.
(Dice rolled, order sorted out).
You: OK (looks at order) Bob (Wizard), it's your turn.
Bob: I cast fireball at the monster (save made, damage rolled, result noted by you).
You: Ok next is Steve (Rogue).
Steve: I take the Aim action (for advantage) as a bonus action, and then I shoot the (CR 10 monster) with my shortbow. Rolls d20 with advantage, hits. Rolls damage, including sneak attack. Damage noted.
You: OK, it;s the monsters turn. It uses its breath weapon, breathing fire on the entire party (rolls dice, saves are made, damage recorded by the players).
Etc.
The above likely goes on for 3 rounds or so, and then it's done. Really struggling to see how it could drag on past 15 minutes in any sort of regularity unless your players need rules explained to them, are not paying attention, or are spending like 5 minutes deciding what to do, or adding up numbers.
Genuine question, how does that take longer than 15 minutes?
Like this:
You: As you walk out of the forest, the (CR10 monster) attacks. It's 60' away, 40' up and swooping down from the air. Roll initiative.
(Dice rolled, order sorted out).
Player: I roll a 7. Oh wait, let me check my Dex bonus. Its...um... +2, to I have a 9. Hold on, I have a feat or skill or racial something that gives me a bonus. Looks. Oh, right, no I don't. I must be thinking about another character.
Player2: I roll a 5, plus 2, that's a 7.
Player 3: Huh? Are we rolling Initiative? What's going on? DM repeats the encounter. Oh, okay. Initiative, that's the d10, hold on. Ok, 8. Do I need to add anything to that? etc, etc. And so it goes for however many players.
Now, as DM, I can put those all in order, PLUS, put in order the monster, and heaven forbid someone THEN wants to add a skill/feat/spell/some other ability to add to someone's Initiative roll. I'm sure its out there.
You: OK (looks at order) Bob (Wizard), it's your turn.
Bob: Looks at his spell list. "How far away did you say it was." "Can you put that on the mapboard/battlemap/whatever". Proceeds to count the squares to double check the distance. Looks again at his spell list. Looks at his feats/class abilities/species abilities, and spell like abilities. Flips through the book or his notes looking for a) something in range, b) something that will do the most damage, c) something that will work best against the known or guessed worst ability save of the monster. Then proceeds to ask whether doing X amount of damage will ground the flyer. Then relooks at his notes before selecting his spell. Then the table discusses what his best course of action is. Then asks AGAIN, about whether he can cast two spells with a bonus action in the same round. THEN, heaven forbid there is more than 1 target, cause then you're looking at 5 minutes MINIMUM of faffing about making sure we got every possible enemy under the AoE for maximum possible damage.
Then we get to roll the spell, save, damage. Then, of course, there is some ability, rider, hex, something that someone forgot about, or wanted to do with a reaction, or whatever. So then we readjust whatever needs to be readjusted..
You: Ok next is Steve (Rogue).
Steve: "How far away is it?" "Can I use my sneak attack if I move under it?" "Can I wait until it passed over, when it swoops, to use my sneak attack then.?" "Well, then I'll move up, jump up with athletics, and make my sneak attack." Or some variation on the theme, which he can't actually do in this moment, but will discuss, look at sheets for some feat/ability/class ability/spell like ability/species ability that will let him do what he wants. Or use "Misty Step" to get onto the flying creatures back, and sneak attack there, while cross referencing his X levels in Paladin so that he can smite the beast too. And then the interruptions as people discuss the relative damage possible, chance of success, etc. Before Steve then possibly changes his mind as everyone is counting out the spaces on the battlemap. Then he uses his reaction and/or bonus action to do something else... etc., etc.
And so on, and so on, and so on. Every round.
Everyone in my last game was multiclassed, which added to the cognitive load. Every single player (and these are players who have been playing some version of DnD for about 40 years) are
piloting their "character sheets" like a jumbo jet or battlemech, pulling levers and pushing buttons to make things happen. And looking for those buttons and levers, or combos of same, for every. single. action. PLUS, not just their action, but their move, action, but wait, further movement as we adjust, cause we can move/action/move, etc., and then their reaction, and bonus action. Oh, and the occassional Action Surge. For every single character to get the maximum bang out of every time its their turn. That is why combat takes so long in our games.
That is also why I went back to Basic/OSE for DND, and the players love it. Simple character sheet. One action on your turn. Things move at a crisp pace.
