A lot depends on the space and how the space is set up and the age of the chickens being mixed.
There should not be an empty rectangle for a run, where every chicken can see every other chicken 100% of the time. I recently added 3 point of lay pullets, with minimal fuss. I do have a rooster, which may or may not help, if he is a good one. But what I know helps is the clutter in my run. I have two shelters set up, facing different directions, I have a platform about 2 1/2 feet off the ground. And I have two large roosts all in my run. I have pallets leaned against the wall.
It looks cluttered, but chickens can get out of reach and out of sight. They can get away from each other.
As to the age of your birds. Your original birds have home territorial rights, and the new 11 are going to know that they are in a strange place, and that tends to knock back their confidence, but there is more of them. Younger birds have less rights than older birds, so if your birds are all the same age, I would expect this to settle quickly. If however, you have birds that are 8 weeks old, and they are full grown, it will be more difficult, and you should take more time.
Generally what happens, is there is a bit of chest bumping, bluster, a bit of peck and run. If that is all, leave them be, but check on them through out the day. Or there can be a heartless pursuit that is kind of horrible. If that happens, what generally is the case, is that there is one or two that are just merciless, and the others follow their lead. If so, pulling them out for a few days generally helps.
Once in a while, you will get some birds that just do not work in that flock. Accept that and sell them. They often work well in someone else's setup. They are not worth the constant strife in the flock. Pull them out, and see how your flock behaves. If they relax, you will sense the tension fall away. Sell that or those birds. If it doesn't, try a different bird.
When you mention space, as in really large, that can be deceiving. If you have constant strife in your flock, which I dispise, sell some birds. Some birds can take overcrowding, some cannot. 15 birds will need a 60 sq foot building - so 6 x 10, 8x8 or something similar. and should have at least a 150 sq ft run, so 15 x 10, or bigger. Currently have have a dozen in 600 square foot run, and I like that. Do not think that 'free ranging' will make up for a too small run or coop.
Just for clarification, you are not quarantining with a wire fence separating the birds. They are all sharing the air. Ten to one, you have visited this person, and she/he has visited your set up, so quarantine is a moot point. You are risking a wreck by bringing in new birds, but if they have healthy where they are, they will probably be healthy with yours, but it is a valid risk.
Mrs K