If you are on an older computer and it gags when you are in Dalaran or join a raid, it might be the sound channels of all things.
Way back in the old days, you'd have 12 of 16 channels. WoW today offer 24, 24, or 64 channels. As it turns out, even 24 channels can bog down older computers. You cannot set it to 16 in-game however. You have to exit WoW, open the config.wtf file, and change this setting:
SET Sound_NumChannels "16"
That must be set to 16 channels in the file. Then re-open WoW. When you reopen the game, hit ESC, click "system", & click "sound", you will see that the sound channels will now be set to a hidden option called "custom". Your Dalaran lag and raid lag should now be gone as well.