I thought that the main problem with runtimes is that if they reside within the Poser application folder itself it will slow Poser significantly, at least in the preceding versions it did.  I have multiple large runtimes in an external folder and haven't noticed an application slow down, it just may take a little longer to navigate the folder tree.

I wish Poser were more like Daz Studio, it's library is alway very snappy no matter how big a runtime.