We recently updated our AD configuration to include a 2-way trust with a number of other AD domains. Since the change our People Picker has been extremely slow (up to 3 minutes) and often timing out. Using the address book function was fine as a workaround but as soon as users typed in the name and relied on the “Check Name” the problems started.
On the people picker you can set various settings to optimize performance including limiting the query to certain domains, site collections. We tried them all with not much luck. In the end we implemented the script below based on a know-issue and KB from MS. The check name now resolves under a second:
Open a new SharePoint PowerShell and run for each web application:
You need to do an IISRESET to affect the changes.
Link to MS KB (worked on our 2010 environment as well): https://support.microsoft.com/en-us/kb/3021471