What makes you think this is related to Prestige? What led you to that conclusion?
Because it's a prestige related action in the client? O.o
Prestige achievement are updated on every mob kill and if you are solo, there are no lags. if you have many people, there are heavy lags... so why shouldn't it be related to prestige?
It's not related to prestige achievements itself or so, but the lags are related to prestige I assume, because of the multiple updates triggered for prestige counters...