If I type letters on the keyboard just after opening Zotero, Zotero freezes and is unresponsive for a few seconds before recovering.
Steps to reproduce:
1) Close and re-open Zotero
2) Select an item in the main library pane
3) Press a letter (for example P)
4) Try to select other items
Then nothing happens, and Zotero freezes. In some cases, the program is not responding at all, with the blue wheel appearing.
Further typing letters works fine. The freezing is mostly observed for the first time typing letters after starting Zotero.

I have 15k items in my library. Is this expected for this size of the library? Is there a way to fix it?

Screen recording
In the video, I first navigate between items, showing that Zotero is working smoothly.
Then I press on P and try to select other item, leading to Zotero freezing and the blue wheel appearing.
After some time, it reaches the item starting with P. I navigate again, showing that Zotero has recovered. I also type multiple times on P, going through the items starting with P successively.
Then I press the letter A on the keyboard. The same freezing and blue wheel appear again.

Debug ID D299386661
On Windows 10 with Zotero 6.0.14-beta.4+32b64b3cf, all plugins disabled.