I consider this a feature. High level casters are not supposed to unload all their spells each day. If they need to, then they need time to recuperate.
It was definitely a feature.
However, certainly by mid-late 2E, spell memorization times, especially as they were annoying to calculate by the 2E method, was one of those rules that had sort of fallen by the wayside for a lot of groups. I remember in very late 2E, seeing it, whilst checking for some other rule, and going "My god, I haven't enforced that for years! Oh well!", and it wasn't just me - I'd played in other groups and no-one had said "Okay let's calculate how long it takes the Wizard to memorize his spells!".
But like a lot of these gradually-forgotten rules, its loss, largely inconsequential in most 2E scenarios, was part of the caster power creep that created the 3E/PF LFQW situation.
I'm planning to put some of the old restrictions back in place in 3e to rein in caster power a bit.
Spell preparation times will be the first. I'll do 2e's 10 minutes/level times rather than 1e's 15 minutes because the math works better with cantrips which would be cosidered 1/2 levels. It's just more convenient to do them at 5 minutes than 7.5 minutes which would either be rounded down to 7 minutes per 3e's rounding standards or 75 rounds which just adds more complications to the math. I'm hoping that will strike a blow against the hated 15 minute workday.
I think you may accidentally encourage the 15 minute workday even more that way, if the mindset is already there, because casters are basically going to want to rest as soon as they use any spells at all, because it's the only way to have a "full quiver" for when the big fight comes.
I think you'd definitely need to make it part of a package, and actively encourage people to engage with avoiding the 15 minute workday in their play, in a stated way, because I don't think rules changes alone will be enough.