Many noted that it wildly swings upon the adventure structure. And it's true. But I'm talking on average, most of the sessions. I've pointed that a "combat-heavy" session of mine usually lasts about 6 to 8 hours, and perhaps half of the session is combat (although the most combat heavy session I had contained only 1 fight that went dire to the players). I think that many of the combat-focused campaigns are made by the inability to actually put a non-combat challenge that actually drain resources of the characters, such as spells or features. I don't believe actually what Xeviat says is true: when you put a challenge or encounter that doesn't have an auto-solution, most players will engage with the situation, trying to solve it as best as they can with all the features they have at hand. Example: a big, windy cliff. Strong winds will knock off flying characters, and the other characters will have to look at their resources, plan and use creatively their skills.
In the last adventure I've DM'ed, a group of 3rd level characters had to navigate a swamp in the middle of a storm (we had a lizardfolk barbarian and an orc fighter/scout, so it was easy enough), followed by a riddle of a Sphinx (the sphinx was too powerful to fight it, and guarded the entrance to a unholy ruin), followed by a very long climb (100 meters to the entrance of the dungeon, 100 extra meters to the seas below) in a windy climate, so things like feather fall were dangerous, and the characters haven't enough rope, so they had to go back to the swamp, use their tools to make more rope to safely climb the cliff, then they had to open a very heavy door, which render the character opening it vulnerable to Opportunity attacks from the other side.
Then was the first combat, that lasted least than 10 minutes, because they destroyed the source that controlled the skeletons. Then the characters had to make a Super Mario Bros platform jumping over a chasm (the lizardfolk carried the rest of the characters, and gained a level of exhaustion), that took more than an hour to they to figure it out, as they were 15 platforms, way more than the monk could jump without exhausting its Ki points. Then the characters had discovered a rolling sphere trap, and discussed how to disable it or if they just risk and run forward hoping not to exhaust themselves before, and that took about 40 minutes. Then the second fight, that lasted even less than the other, as it was basically the same but without a chasm to pitfall the skeletons (the rogue shined here, as he disabled the mechanism). Then they encountered the rival group prior to go to the boss fight, and they parley and trick the other party to fight first and soften the monster (the 4el monk also snuffed out the torches and bonfire of the other party to allow the rogue sneak in to see the boss monster, and they decided afterwards). Then it was the final fight, against as chuul, that took a little longer (the chuul used its grapples to grab the monk, paralyze it and try to drown it, but the lizardfolk rescued it), while the rogue recovered the artifact.
In total, in a dungeon crawl, they take less than one hour fighting, in a 6 hour session. But that isn't unusual on my experience. (Sorry for the long recount)
It was in a convention, so even when two of the players were friends of mine from different tables, the other two were amateurs on 5e: one (the lizardfolk) never played D&D, and only played WOD before, and the other one (the rogue) is a 3.5 DM. The WOD player came surprised, having the (wrong) impression that D&D was all fight and no roleplay, and he liked a lot how we play. The other players had varied experience with D&D (the orc is my DM in one campaign, and a player of one of my campaigns, the monk is a regular player in a relatively new campaign), and neither of them came out very surprised on how much fighting was (except the 3.5 DM, that praised the speed of play of 5e).
Again, tl;dr: we didn't come on all that much fighting, and fights, although they may be deadly, take a lot less time to resolve than other challenges, like the platform jumping (the image below shows how it was-sorry it is in Spanish).
