it works just fine
Clearly, it doesn’t, and it is a miracle that it works even badly. Indeed the code is such junk that what you are trying to do is far from clear.
For starters, you are using software serial on the hardware serial pins, which is usually as fatal as this is.
Secondly, your chances of running software serial at 115200 are about zero.
Thirdly, however you do it, if you want to run Bluetooth at 115200, you have to configure it to do that, and I’m betting that you haven’t.
Fourthly, the only evidence that you might be using the serial monitor at all is in reply#1, and why he would guess that is beyond me. There is nothing in your code to that effect. Serial monitors use serial commands, not software serial commands, but at least you can’t wire them incorrectly. I suggest you ditch the junk code and start over but, before you do that, you must clearly work out what you want to talk to what via Bluetooth. There is nothing to suggest you have done that and, as things are, I rather suspect Bluetooth is not being used at all, rather like the wire library. I also suspect that you didn’t write the code, you just picked it up some ancient junk from someone who had no idea of what he was doing - which is unfortunate…
You might try the following notes
I don’t have any better idea of what you are trying to do than you do, or even of what Bluetooth you are using, but you may find some background of what Bluetooth is about.