The 115kbps figure is most likely to be the DTE rather than the DUN speed - entering W2 in the modem's Properties Extra Settings box will correct it.
You can find plenty of help on modems and all things related at:
which apply in general to modems in most countries.
I suspect that a better driver could be found - try the manufacturer's website or one of the websites providing drivers such as:
Username is drivers2 and password all