Nested timelines incredibly slow

This might be a difficult one to look into but it's made my existing workflow too painful to use so I'm hoping perhaps there's something I can do to resolve this.

My current workflow is to create a timeline with 5 to 9 different angles in it, nest all of those and enable multicam. I then go through and cut the multicam project together. When this is done what I've always done is put this timeline into a new sequence to cut, apply filters, add titles etc. Unfortunately as of a couple of months ago I can no longer really do this without the final step being incredibly slow. It happens no matter what computer I'm on - my desktop is fairly powerful and still crawls to a halt. CPU usage peaks at around 7%, gpu is basically at 0% and it's using about 1.5gb of 32gb ram so I'm not sure the hardware is the issue. Is there any way to resolve this?