My Warlock player has Pact of the Chain and likes to explore all the dungeon before going inside. The imp turns into an invisible spider and goes through the ceiling to all rooms without hard doors. In practice, this ends up becoming a 1 on 1 conversation between me and the warlock, describing each room, for about 10 minutes until all possible rooms are revealed.

To speed things up, I have the familiar roll a single Stealth check before entering and I compare that against Perception checks from Guards and Passive Perception from all other NPCs (I usually apply disadvantage to these checks, since it's a spider and invisible). I still feel like it's a slam of exposition that bores the other players at the table. When the party is going room by room, exposition is broken down in separate parts, and the risk engages the players. I've tried to ask each player to control the imp at each part of the dungeon, but players didn't enjoy it. I also like to add important bits of information at each room (like a Guard using a secret password here, or toxic fumes there), which ends up taking even more exposition time.

One on hand, I want to reward the Warlock and his methodical exploration. On the other the other players are just standing there doing nothing while the imp explores. How can I make this part of our game enjoyable and engaging for everyone?