Nostalrius Begins - Quality wow vanilla realm (1.12)

Hey guys, I've been experiencing extreme lag for about the past month on Nostalrius. It typically happens when there are 12,000+ people online. Are there any fixes to this? I am unable to farm or do dungeons most days, because as a healer, my Healing Touch needs to cast faster than 8 seconds for Rank 4.

Any fixes for this lag? Anything I can do? This is getting unplayable and I play Nost every day. It's not gotten better unfortunately.