Lets stay on topic. I don’t need concern. I appreciate the people with their kind honest answers.

I typically play 14-16 hours a day.
(p.s. I don’t remember. I completed that achievement over 10 years ago.)

Lets stay on topic.
Agree, we don’t know your life or whatever.
Anyway did you decided to try?
took me several weeks . . . but that was during Cata when there were of course less quests to do . . .

I’d be shocked if you didn’t complete one expansion daily at that rate.
That’s a little difficult to do with Vanilla.
The hardest part for me was finding some of the hidden quests, like the gnome NPC who shows up at Nessingwary’s camp in Nagrand every 30 minutes or so. Also, many Cataclysm revamp zones have you taking a mob down to low health for capture without killing them. That is extremely difficult to do on a high level character,
Loremaster is pretty straightforward until TBC. There are some quest strings in there that are really confusing.
Also, it’s the longest of the expansions. Lots of flying from one zone to another
After Wrath, the expansion get a lot easier. Especially from WoD forward, when “Loremaster” was required for Pathfinder. In those, Loremaster just means do the main quests where as before that it pretty much meant do EVERY quest.
Eastern Kingdoms and Kalimdor for Vanilla are the real time pits, just because of all the travel if nothing else.
Pretty sure I’ve got Loremaster from BC on, but I have not done EK or Kalimdor yet.
They’re a lot more fun being around the proper level. But I just loathe going to low level content and one shotting everything with a glance. That may just be me.
Once you unlock it in any expac then it will always show as you having it unlocked and then only the regular quest achieves will show after that. If you wait until now to unlock it then you have to do all of DF+ all the others in order to unlock. I unlocked it in the past so it shows that there is no loremaster to unlock now, only the quests for DF to do to get achievements for those separately. The longer you wait the more time it will take.

. Also, many Cataclysm revamp zones have you taking a mob down to low health for capture without killing them.
There’s a Foam sword toy that does this for you. They sell it in capital cities. https://www.wowhead.com/item=137663/soft-foam-sword
Actually simple with the way vanilla zones are tracked now, i.e. Blasted Lands Quests only has 3 objectives. Sure, each of those is a mini quest line but with a bit of wowhead to get you started, you can knock them out easily and very quickly with a level 70 character.
Now, if the OP is doing it while leveling, or with a lower level character, I could see more difficulty. But I didn’t get the idea they were going to be spending 15h daily on a low level character if their aim was to get all 12 loremaster achieves.
Heya I got Loremaster done a month and 18 days ago.
I made weekly-monthly goals for each expansion on this character.
Relatively fast ones felt like Cataclysm, MoP, BfA and WoD and Legion.
Relatively slow ones are BC, EK/Kalimdor (sheer numbers) with WoTLK being in the middle but very fun. If you haven’t done SL/DF they will take a long time since sojourner take a while to do (but are also some of the best - you dance with a trickster, teach a lil owl guy how to fly).
70% of my Loremaster journey was done as a Marksmanship hunter. It is nutty what sort of shenanigans perm movement speed out it combat + barrage can do.
My problem with getting loremaster now will be how slow non-DF flight is. Not sure I can handle it for so many zones.

you can knock them out easily and very quickly with a level 70 character.
Now, if the OP is doing it while leveling, or with a lower level character, I could see more difficulty.
That’s fair. I’ve honestly got a lot of Vanilla zones left to do and I haven’t tried for Loremaster because of it. I should give it a go.
I’m working on it on an Evoker. Soar sucks in dragon isles but it’s pretty nice in old flying zones!
So I’d like to give a good answer because I’m trying to work on this one too and I have only completed two of the requirements, Battle for Azeroth and Eastern Kingdoms. I play through the content, read the quests myself because I like to learn the lore in the game as well as play it.
I play on peak about 10 hour days a few days a week just because work permits, I also play the dungeons and raids of the expansions. When I go back now to do it, it’s trivial yes. I also do achievements sometimes, like I’m doing Warlords of Draenor’s “Warlord of Draenor” title achievement and Nemesis questline (not required), just a Draenor cleansing.
Using BtW Quests, I would do a hot take and say it would take me personally 3-6 months on trivial content just because I like to experience it. Like the Garrison, all the places and some side questlines that are fun along the way. I also collect transmogrification weekly from old raids along the way and I’m still to this day working on Thunderfury.
If you just used BtW and did nothing else, didn’t even read quests, probably a month. If you did read quests, I’m gonna stick to anywhere between 3-6 months. Everyone has a different schedule.
It took me roughly a month and a half to finish Loremaster. Most everything was super easy and quick with the exception of TBC
Race each other
I don’t know. Not long, though. It’s one of the easier and more casual “grinds”.
Depends on if you read the quest text or not I’d imagine.
If you’re just speeding through it, eh. A week?