First of all, if you want a user to have unrestricted permissions in Adaxes, there is no need to use security roles. You can add the user to the service administrators list: https://www.adaxes.com/help/AddRemoveServiceAdministrators.
Using a business unit will not work better. Also, it does not allow you using OUs as subtree, which means that you will need to add all objects (user, groups, subOUs, etc.) to the unit explicitly.
Such slowness can be observed when you have lots of security roles (100+) and lots of assignments (200+) in a role. In your case, the slowness does not seem to be related to user permissions. To help us troubleshoot the issue, please, provide the following details:
- What operations are performed slow? What about logging in to the Web interface?
- Are the operations also slow in the Administration console?
- Did you try to sign in with the credentials of the Adaxes service account (specified during Adaxes installation)? Is it also slow when performing operations as this account?
- On how many computers is the Web interface installed? On how many computers is Adaxes service installed? Are the Web interfaces and Adaxes services installed on the same computer(s)?
- Do you have at least 1 DC for each managed domain in the same AD site as Adaxes?