It’s really the DM
…and you might need to find a new table
You are asking about a problem player who talks too much, but your bigger problem is the DM is holding just as long a conversation. It’s the DM’s game to run, and to set the pace of the game. It’s simple enough for an NPC to stop talking to a loquacious PC — if the GM wants to.
The two of them, at least, seem to be having a fine time doing deep role-playing. It’s a legitimate play style — everyone finds their fun differently.
Appealing to “realism” won’t work
Imagine you and your friends were really going to confront a squad of evildoers tomorrow, in a life or death struggle. You might stay up and go over your plan again and again, just because you can’t sleep.
And this isn’t necessarily bad narrative. Henry V, Act III spends several scenes on the conversations of soldiers and knights on the eve of battle, discussing military protocol, the ethics of warfare, and boasting about their horses.
If the NPC in question has a personal interest in the outcome of the fight, it’s not unreasonable they would be willing to abide with the heroes for hours.
For you, the long conversation bore you and breaks immersion. For your co-player, it seems to do the opposite.
What do the other players think?
You haven’t mentioned the reactions of other players at the table. If you are not 100% sure what they think of these long talks, find out. If everyone but you is having fun the way the game is now, then it’s probably time to just move on.
On the other hand, if a good portion of the table is seriously bored during these talks and is champing at the bit to start rolling dice, then you (as a group) might speak to the DM about speeding things up a bit.
Finding a compromise
Out of game, just say that you’d have more fun if the game had a higher action-to-talk ratio. In game, when a “strategy session” has been going on for a good long time, your character can point out when you think things are sufficiently hashed out, and since things never seem to go as planned anyway, you might as well get to it while you’re still fresh and can think on your feet.
Be aware, though, that there will always be a compromise at this table between those who get a charge out of strategy sessions and other long talks, and those who prefer to pick up the dice sooner.
Dropping Hints at the Table
You seem pretty steamed right now; you probably want to get in a more amicable mindset before broaching the subject with your GM and co-player.
If you come to an agreement-in-principle that everyone will try to limit pre-battle talk, your characters can remind folks when you are ready to move on. A few lines I’ve heard:
- A swashbuckler (predictably asks): “You do-na' thing we could-a speed things up?“
- A barbarian interrupts: “Conversation is silver, violence is golden.”
- A slightly-unhinged paladin cheerfully agrees: “All’s well that ends violently.”