Yeh can increase the performance of questhelper by going into yer alts hit map, upper right hand corner click on it.
It'll still display all the quest info for yer alts on yer main but it'll stop calculating routes for em all.

plus what helps is /qh settings there ones that yeh can reduce how much resources it uses to calculate the routes.
I just end up turning of the route planning thing all together its just easier to look at the map real quick anyways