I am experiencing huge lag spikes in the Nether Fortress and its vicinity, most noticeably when several blazes are nearby. It seems that when I kill every one of them my framerate becomes more consistent. Also for some reason they are able to track me through walls and shoot repeatedly that also contributes to this issue.

As far as I can tell, it may have something to do with their sound, because a very long time ago I noticed that when a blaze spawner-based mob farm accumulates several blazes it drops framerate much more significantly than any other spawner-based mob farm and also disables all sound apart from the burning sound that blazes emit.