I can't really tell, I haven't experienced what you're describing. In fact heal rk is one of the roles that I feel comfortable playing with lag.
It could maybe be related to the effects stacking by HoT and all that, as on healing you see way more numbers all the time on your screen and maybe your RAM saturates faster.
Could you tell if you're using 64 or 32 bit client? I play on 64 bit and it's true effects stacking caused way more lag on 32 bit client than it does in 64 bit.
Thanks for reply mate!
I think found the problem. It was one of the plugins. I was used to load AltInventory to be able to check alts storage. Neat thing, but why it causes so big lags while playing RK heal i had no clue at all. Unloaded it couple days ago and I can play RK heal much longer. Got no such lags anymore. Well.. if that helps anyone..
BTW Using 64 bit as long as it was created finally. Works awesome. Hardly got any crash cause memory since then.