VTTs are really bad at exploring dungeons.
The way I learnt was that you had an exploration map, drawn by a player, and you might get out minis and draw the room if necessary. You could do something similar with a VTT, have some of scaling map where a single token represents the party and then scale that down, but there seems to be no interest - it's all about the battlemaps. (And I've seen this approached used on the table top too, with the party moving through photocopied maps that get laid out as they move along)
There's a few ways I've found to approach this problem. These are not all meant to be used together. Some are combinatory, but some are alternative approaches.
1) Change the way dungeons work when interacting online. Think a bit more like a computer game designer in regards to locations (especially old school ones where scale was limited). Instead of having lots of rooms with one or two things each, have fewer locations with many things each - even if some of these things seem to verge on implausibly close. A room the party pass through in five minutes on the table top is fine, but if you're prepping a map then it's a wasted map. Instead of putting something in a room, stick it in a nook or alcove. Try and give the illusion of size and scale while actually cutting back.
2) Don't put some kind of art or token to represent every single thing on the map. This tells the party that what they can see on the map is all there is. Put numbers or question marks or something to tell them that there is something there, but they need the GM to tell them exactly what is there.
3) If you want the feel of a vast sprawling dungeon - rethink what exploring means in the context of the VTT. It's tiresome and tedious to have the whole party exploring a huge mapped out dungeon, if most of the space doesn't have much in it. So intead just present the map as a whole with a single "you are here token". At the beginning use fog of war to make most of the map blank - but simply put numbers on the map to the nearest major room location and let them choose, and then skip to that map (approached like 1 above), avoiding wasting time on maps of corridors and the like - just work with assumption there's little of interest in those places. If you want wandering monsters have a separate corridor battle map you can switch to for that.
4) Consider turning off the dynamic lighting. The dynamic lighting basically prompts people to move their token around all over the place to see what's there. If you just turn it off people can basically see what's there to see (unless you've hidden) it, and the pacing actually returns to something more natural. You can always hide monsters in the GM layer and move them forward when the party tells you "we go around the corner" - instead of having one player suddenly move their token around the corner and make the discovery of the monsters through their lighting, while you are busy trying to resolve an action another player is in the middle of.
5)Just go minimalist. If you're using video you really can do away pretty much entirely with maps and go as minimalist as you like once everyone gets used to it. If you're just using voice, then it helps to have something to look at. But you can run a whole game sessions with maybe a mood board of images, that you occassionally refer to. Be aware that images can actually be problematic, because a lot of players may not be looking at the VTT if it doesn't seem urgent - they could be looking at their character sheet, or checking a rule etc.
6) Overreliance on beautfiul maps and images can be a trap. You become stuck with what you can find maps for. Good luck with that if you want to try anything that's not generic - you'll end up spending a lot of time looking for maps and images - 99% of what's there is pure generica. You want an Arabic city, or an Asian temple or castle that is not Japanese? Or even a medieval merchants house? (Go type 'merchant's house' into pinterest and you'll find a whole load of Victorian homes). Good luck!
7) On the other hand, you can run a whole wilderness adventure with just a single map of the region as your background for pretty much the entire session. Players seem happy if they have something that basic to look at and orient themselve. If you do switch to combat you just switch to a terrain based combat map (and these are pretty easy to find). Maybe consider whether on the VTT it's worth spending more time on wilderness adventures and less on Dungeons? (Especially as it's easy to put a small dungeon like a ruined temple in the wilderness and these work much better on a VTT).
8) Like on the table top not everything needs to be done with maps and minis. Theatre of the mind is still viable. (And you can use the draw function to sketch things out quickly). How are you going to handle a combat that you didn't expect and didn't prepare for if you are too reliant on prepared maps?