Apologize for late response.
Actually it’s a known issue with 0.25.x version. It may be vary from user to user. Like if it’s open previous sessions, long history entries, etc.
But I can confirm that the new version, 0.55.x and up are working faster.
Automatic update for the current users is coming in weeks, if not changed. But if you want, you can download it now via brave.com/download
You can then import your browser data (but it’ll not import your Brave Rewards wallet, yet, if you have one) from the current Brave. Note that this version is still work-in-progress so may have missing features.