Is there an optimum? Just one sentence might have too much overhead, there might be a maximum size for LT. Is there an optimum somewhere in between? At which size roughly?
I don’t know whether that’s the optimum, but for many automatic tests we concatenate 10 sentences before sending them to LT.
I might do a local test multiple times, because of all caching involved.
My local server showed the shorter time per sentence around 1000 characters. A remote server close to the max.
So no real conclusion.