iMovie became very slow after updating to MacOS Sequoia 15.4

Before updating to Sequoia 15.4, my MacBook Pro was on 15.1 and everything was running smooth. I was able to edit 1 hour long video (approximately 1.5 GB size) in iMovie without any problem. After updating to 15.4 - the whole laptop became slow. Even if you open 1 hour long video in Quicktime - it's not able to render it and iMovie not responding when adding 1 hour long video to the timeline. My laptop has around 115 GB free space and 8GB RAM, 1.4GHZ Intel Core i5. All these problems started after updating to 15.4. I searched internet and did all troubleshooting like resetting PRAM, SMC, disabling Siri and other unwanted services, etc. but it's not helping. If anyone else facing same issue with 15.4, and was able to resolve it, please suggest how to solve it. I also sent iMovie error report to Apple. Downgrading to older version is not an option at all because its very time consuming and its not easy. Looking forward to hear from community on the solution.

Another issue I started facing after updating to 15.4 is the gliches / shattering in the voice recording. When I record voice using an External USB mic and Quicktime, the audio is shattering and it has glitches like some part of recording is not audible. It's all due to high processing / CPU usage by Sequoia 15.4 I guess. This problem was not there before 15.4.