RadScheduleView control is not foreseen to work with such a big number of resources and adding Special Slots to those resources could cause performance issues. There are some measures that could be taken into account when using Special and Readonly Slots
and they are specified in this
help article under the Important section. But even if those measures are taken into account there may still be performance issues as the containers that are rendered for all the Resources, VisibleDays and Special Slots are around 30 000 elements.
the Telerik team