You definitely will get implicit conversions, which can be a huge slowdown. I'd fix this first.

The plan shows that the inserts to the AuditLog table, and then the full text table update and insert are the slowest parts. I'd work on the conversions first, and then see. I thought the FTIndex wasn't supposed to be an issue. It could be slow to catch up, but I didn't think it would cause slowness on inserts.