You can use a top-up sync strategy to speed up syncs enormously
Let's say you run a top-up sync every 1 hour, then you might do
rclone copy --max-age 1h --no-traverse /path remote:
To only consider files which has changed within the last hour.
Then once a day (say) you run a full rclone sync which will sync deletions and anything missed.
You probably would want to use --no-traverse for this but it might be faster without if all the updates to files tend to be in one directory.