Thank you for your question. Unfortunately I don’t think you’ll be able to speed this up. When you use Remote Mode GroupWise needs to do significantly more work when you added a new message to the message store. (i.e. it needs to build remote requests and phsically write the entry to your remote database). Depending on the size of your Remote database, this is going to take some time.
I’ve had a look at your code, and can’t spot anything that looks slow. Unfortunately, I suspect the delay is just an unfortunate side effect of using Remote mode with the Object API.