Timeline operations get unacceptably slow when presentation size grows

Adding children and changing slides is still annoyingly slow when presentation is large. For example, when running in debug mode, adding a new object to slide with 25 objects in it already takes 2-3 seconds, and changing to master slide and back takes about 10 seconds.

The performance needs to be checked with release build, but since the time to do operations seems to increase exponentially when the number of items on a slide grows, I suspect even release builds suffer from significant slowdown when presentation size increases.