Some groups play a lot faster than that. The main group I play with did a 1-20 campaign is about 3-4 months. We finished the campaign (Moonshae Adventures) the end of October, that campaign started in July I believe. Tonight will be the 5th session on the next 1-20 campaign (Dragonlance Unity of Shadows) that we started in November and we are currently level 6.
I think we completed all of Dragonlance SODQ, start to finish, in 7 sessions.
Another group I played with started a 1-20 campaign (Doomed Forgotten Realms) in February and finished in July. We followed that with Storm King's Thunder which went 1-10, we finished that campaign in September and started another 1-20 (Shattered Stars) and are currently level 13 in that campaign and will probably finish in late January or early February I imagine
I will say high level play starts to drag for me and levels 15-20, so if it took a month to gain a level I think it would disintigrate.
Between planning, playing and DMing I spend about 30 hours a week on D&D. 'That does not include time on this forum.
I think that's a good deal faster than most tables, and also points to D&D not needing 20 levels.
If you're roaring through 20 levels in 4 months, and you play 1/week, that's a level per week, one level per session, one level per four hours or so of play time. I wonder how many monsters you get through in that time frame, how many dungeon rooms, how many class features or spells get used vs. how many sit gathering dust on the character sheet. In other words, how much content are you using?
If D&D just had 5 levels, and each level was a bigger jump in power, more focused on the content you use, how much smaller and cheaper could the core books be?
Of course, there ARE tables that use all that content in a small time frame, I'm sure, just as there are tables that use a much longer time frame to do the same. There's natural variance, which means there's a balance to strike between granular and chunky levels, to be sure. One where a fast table and a slow table are still getting good value from the same ruleset. My inclination is to say the balance is a little too much on the "granular" side today, that there's a lot of content that just doesn't get used, often because it takes too long in actual play for it to come up. I imagine going through levels faster would highlight that problem - there'd be fewer instances of more niche features and spells, overall, and a lot more unused content.
30 hrs on D&D a week is almost a full-time job. How many hours per week should D&D be made to play at its core? I don't think 30 (though, y'know, I don't think we need to abandon the 30+ hrs people, either). I think more like 4.
It would be better for business if players could easily start higher level campaigns.
WOTC could dump out a brunch of feats, items, and subclasses and payers can start a new campaign with a bunch of them.
I think this idea's got some legs, but I do think that the audience is limited. "Number gets bigger" is a compelling game mechanic, and you don't see that growth if you're starting at level 17. There's also a pretty significant amount of detail and complexity for high-level characters that is easier to handle if you see that character grow, and can be easily overwhelming if you just start the game that high. And then there's the sort of instinct to start at the beginning that's going to make "level 1" appealing regardless of how powerful in the world we define Level 1 to be.
If we wanted to start high-level campaigns, we might be better off defining what we want out of high-level campaigns (teleportation? big damage? dragon-slaying?) and making those more possible at lower levels. Or just getting some of those aesthetic elements in for a particular adventure and assuming the players start with them in that particular adventure.