The org. tree is quite slow, but the speed is unpredictable.
Right after midpoint start and first login, browsing the org. tree takes several second to actually open the content (right side panel) of the organization.
I have at most 50 organizations, no deep structure. The issue is even in flat organization structure. It seems to be related to the number of objects in the organization (in my case, 1-5 users inside org).
Expanding (+ icon) organization is fast.
In time, the performance improves; maybe some caching?