Hiya.
I really, REALLY wish I knew how you managed that.
I spend around 10 hours per session building encounter matrices, writing miscellaneous notes about each encounter (to prevent referring back to the adventure constantly and help keep the flow of the session rolling), and detailing treasure and XP for each encounter. This doesn't even count maps or other work I could/should be doing.
I must ask - how did you manage to whittle it down so much?
The big question is... do you
enjoy doing 10 hours of prep for your game? If the answer is "Yes!", then keep on keeping on.

If the answer is "No!", then you need to cut down on the stuff you don't 'need' to have at your fingertips.
If you are writing all your own material, I use a "point form" method. I don't write out whole encounter settings, I'll just give it a descriptive name, then a few point form words to help me ad-lib it when the PC's get there. So...
- Midnight Kobold Ambush
- Swamp, fireflies, spooky sounds, ground mist
- Big, moss covered log cover; hollow, see through holes, treasure inside
- 5 Kobolds; javalins first, then attack
- Crypt Key, 24cp, dead rat, dried chicken feet
That's all I need. I don't need to write down DC's for anything, or the effects of various environmental things like obscurement and ground cover. I don't need all the "extra" words (e.g. "The kobolds treasure is hidden inside the hollow log they were hiding behind."... I can get away with "log, hollow, treasure").
Just writing the name of the creature with the book/page is all you need ("Kobolds x5, MM195") is good enough.
Basically, you don't
need to have all the information written down in front of you. The 5e D&D books are for reference, so use them that way. One thing I have on my custom made DM screen is a small little section with page numbers in the DMG of where to find various things that may come up every now and then (like NPC's, Environments, Treasure Hoard tables, etc).
If there's one thing I learned playing this game for the last 34+ years (since '80), it's that the more you reference something, the less you'll have to reference it in the future. Back in my 1e DM'ing peak I could tell you the page number in the DMG for just about anything...Combat Tables...pg 74; Saving Throw Tables...pg 79; Hiring NPC's to cast spells...pg 103; Sage Information...pg 31. The list goes on and on. By using the "reference page method" you will reinforce your ability to recall rules, numbers and all that other stuff, or at least blurt out "Hey, Curtis...flip to the Feat section in the PHB for me, page 165"...and then continue running the game with the player who isn't waiting for his turn or whatever.
I think the core thing is... those of us who "prep with little pages", only prep by "roughing out" stuff, leaving the actual details to happen naturally, during play. For an example of a nigh-perfect example of this, check out Dyson Logos's
Dyson's Delve adventure PDF (free). It's a pure dungeon crawl of 11 dungeon levels (
https://rpgcharacters.wordpress.com/maps/dysons-delve/ ). It's room layout/description is the perfect mix of info and vagaries. I ran a game (using 1e AD&D) just last year or so with this. Campaign lasted about 8 months with this puppy...and they only got down to level 7 or 8 I think! Ton's of fun, lots of RP'ing (nearby town, gathering information, encounters with another NPC adventuring group, a bandit group lead by a witch looking to use the caves as a base of operations, etc...), all with an underlying quest I tossed in; find and retrieve (hopefully alive) a young 8 year old boy named Willem who ventured into the caves to spite his parents. Good times...good times...
^_^
Paul L. Ming