Honestly? Practice, practice, practice. The more you read braille with proper technique, the better you'll get at it. Being able to read fast isn't necessary to speak. You don't speak super fast when you talk, and you certainly shouldn't during a presentation. One thing you can also try is using speech to read. If you have a device with text-to-speech, slow it down until you're comfortable, and then edit read it by sentense or line. If you can read by sentense, you can actually edit your document and replace all commas, semicolins and other breaks with periods. Then you can read pause by pause. Read it aloud to yourself a few times in this manner, as if you were reading it in class. A combination of memory and this method may help you sound natural. Source: I'm a voice actor who can't read outloud very well, and this is what I've found works for me. I've also given several talks and presentations this way too.

As to reading: that will only get better in time, and perhaps like some blind people I know you will have to rely heavily on audio books and screen reading programs (although Braille is my personal favourite) .

As to giving presentations, how long is your presentation and have you considered doing your best to memorize it and just having a Braille cue card to refer to?

When giving presentations it’s better not to be reading straight from a page anyway
What I have don in the past though is print out my notes as large as needed but write them in short hand so it’s more of a word or short phrase that reminds me of what to talk about next

You could do something similar with Braille if you read that faster and just have a sheet with a few words per topic double spaced to make it easier to find your place

Hope this helps