I have Yuko my Blue Crown Conure and for the most part she is quiet. She talks some and very rarely does the Conure scream. My girlfriend was thinking about getting her a Blue Crown or a Sun conure. With there being more than one conure in the room would it cause them to be loud of there was two in separate cages?
I have 1 blue crown and 3 green cheeks. The blue crown was the latest addition, fearing the GCCs would all scream in jealousy (but they didn't). I used to have parrotlets with the (then-newly acquired) GCCs and the GCCs would scream every time I went to play with the parrotlets, which is why I worried they would not get along with the BCC.
Early on, after getting the blue crown, it would scream at times and the GCCs would not chime in. Or the GCCs would scream and the blue crown would just sit there, waiting for the sun to supernova or something.
Now that the blue crown is bonding to me, like all the others have, they all chime up in unison. But they still don't call back and forth to each other, which is amazing... but then, all of them are typically quiet, and when one calls out the others just don't follow.
Oh, I live in an apartment... the BCC's typical scream is on par with the three GCCs' loudest. The BCC tends to be quieter on average, unless he's really onto something. If I had a sun (never in an apartment) I could fathom the BCC trying to compete, to match a sun's level...
Your situation may vary... especially as Suns are far louder, and far more frequent with vocalizing in general... the BCC might pick up on that and start doing the same things... (As was said, the only way to know is to try -- is there a return policy if things don't work out?)