Li Shenron
Legend
I have been gaming for more than 20 years, and I have never seen this "fifteen-minute day" problem. My players have learned the hard way to conserve resources.
Same here.
Maybe I'm doing it wrong, maybe I'm being unfair (or just plain stubborn.) But this is a D&D adventure, not the "Everybody Watch My Awesome Wizard" show.
The limited number of spells, etc. is a feature, not a bug.
We must have had badwrongfun

Me too feel like a traditional D&D adventure is having a Fighter who fights, a Cleric who heals and protects, a Rogue who sneaks and handles traps and lock, and a Wizard who can go beyond human capabilities and do what cannot be done with mundane means, but the power of the latter is compensated by the limited resources.
When a game doesn't accept this concept, and want to switch to another concept that is "no resource limits", it is then unavoidable that it must also change the concept of magic to go beyond mundane means otherwise the Wizard would be easily dominating the game. Spells need to be toned down somehow and the risk is reducing the Wizard to a Fighter with a different flavor. It's fine, but it's a different game, and for my own tastes it's an inferior game setup because you have one huge diversity option less.
Instead, 5E should just give each character a certain number of points, and give each of these superawesome superpowers a point cost. Done.
We already have points, we just call them "slots". You may want to explore variants, and if you e.g. add a simple rule that a higher level slot N can be swapped for a number of lower level slots the sum of which is N, this already allows the player for more control over focusing her firepower on a shorter or longer time frame.