What do you play as Black against the Queen's Gambit?

Really it depends on what time control you use, but 15/10 is the middle one, so... 
Maybe if you're playing 10 minutes. Okay so in that case you've spent only like 12 typical RPG games worth of time playing.

Pirc

Do you mean the King's Indian Defense?

If u want break the magic 2000 barrier, you will prob have 2 play .1Nf6 .2pE6 /then pick an indian defence. If u feel like u are a hypermodern player, u can try the QG accepted. You will give up more draws and abandoning the center is risky against masters./ but there is a reason top players have always played the QGD (with white) for over 120 years..,

later dudes

goommba88

It's worth learning the QGD from both sides.

After playing the Tarrasch Defense (a variation of the QGD) and Scandinavian for years I recently made the difficult decision to throw that all away and 'upgrade' my repertoire. Now playing the Nimzo/Bogo and French.

The Bogo is a strange 'upgrade', but whatever makes you happy. The Queen's Gambit declined is the most played opening in world champion matches, so has never been a beginner opening. Recently ways have been found to deal with the Botvinnik plan in the exchange variation etc, so has never been in better shape theoretically speaking.

The Dutch is not a response to the Queen's Gambit. Neither are Indian openings or weird countergambits.

While you're correct, I think generally the question is what is the defense against the mainline d4-c4. It's a bit weird when considering move 1 answers, but if 2.c4 is the mainline I think it fits within the spirit of the question.

Mind showing us these new plans in the QGD exchange?

The new plan is playing b5-b4 in reaction to f3 preparing e4, making this as hard as possible for white to achieve. The knight goes to the queen-side with Nb6, instead of traditional Nf8-e6. Often black will play Rc8 and c6-c5 later.

The more traditional 11f3 c5 of Botvinnik v Larsen hasn't been refuted either.

You can see more in books like "Countering the Queen's Gambit" and "Keep it simple for black".

Two suggestions I will comment upon:

I like the Tarrasch for black. The Hennig Schara Gambit is a valuable surprise weapon. If I knew that white would play 1d4 d5 2c4, I like the options open to me via the Tarrasch.

I do prefer the QGA as black because after 1d4 d5 2Nf3 Nf6, white can transpose with 3c4 or play something inferior. I even like 1d4 d5 2Nf3 c5 for black. This guy gives an interesting two video simplified QGA repertoire for black that constrains white with transposing lines in the case of 1d4 d5 2Nf3 c5 3c4 dc or 1d4 d5 2c4 dc 3Nf3 c5. He also deals with "annoying d pawn" variants...

https://www.youtube.com/@gmalexcolovic/videos

I do like the idea of narrowing down responses from the other player.

When I played the Queens Gambit as white for a few years, acceptance of the pawn was rare. I felt a certain dread about facing the QGA since I was hoping for a more mechanical Exchange Variation that I felt, rightly or wrongly, could be played on auto-pilot. The QGA demands attention. So white won't necessarily be booked up on an opening that leads to open positions and piece play. In practical play, those more familiar with the position might do better. OTB I have held my own as black against higher rated players than myself.

yeah after toying around with the Slav and the Tarrasch - both great openings - I went back to the QGA. The midgame of the QGA just feels very easy, there's not the same counterattack as in the Slav, and black isn't on a timer to make something happen like in the Tarrasch

Looks pretty good, but White usually delays f3 until after castles. What do you play here? Just Nh5? Or do you play a5 > b5?

Both are playable 11...Nh5 is safer and more positional can see both options mentioned in notes to 3rd game of recent Nepo v Ding WC match here https://www.chess.com/news/view/fide-world-chess-championship-2023-game-3

Semi-slav

RE. the three "good" responses, e6, c6, and dc4, I believe the best thing to do is to try each of them and see first, how comfortable you are with each and second, how successful.

Not a lot of people accept the Queen's Gambit, so it is entirely possible someone who isn't used to it can have something like this happen.