I'll add my welcome to
jennifac. Welcome aboard!
I'll also add my frequent reminder that as a new user, they can only make 5 posts in the first 24 hours and so will be unable to directly reply further until that time expires, I'm sure they will catch up on any further help that can be offered.
It seems there are 2 questions:
a) Will there be WiFi?
b) If there is WiFi will there be enough bandwidth (in layman's terms, is it fast enough)
To the first question, BA is currently in the process of rolling out WiFi but the majority of aircraft don't have it yet. There is a specific post with details of which aircraft are known to have it:
https://www.flyertalk.com/forum/brit...-underway.html
See the wiki at the top for specific details. Looking at that, we can see that 8 of the 747 fleet have been equipped, but here comes the bad news......
All of the 747s with WiFi are the so-called "86J" variants which are the ones with the refurbished larger CW cabins and improved in-flight entertainment. And as far as I can tell Las Vegas is only ever served by the older "52J" 747 variants, none of which have WiFi fitted at at this moment in time. While unfortunate, it is perhaps not surprising that BA use their older, tattier 747s on that route - I can recall one insider here commenting that the ideal LAS plane would have a cabin made entirely of stainless steel so it could simply be jet washed down at the turnaround
So, the chances of WiFi would seem to be between minuscule and none. The only scenario I can think of where it isn't none is if they had to swap in a last minute WiFi equipped 747 at the last minute due to technical issues, but even then presumably they would look to another 52J variant first to avoid seating hassles.
The second question becomes somewhat moot. That said, perhaps the performance might be better than some fear (based on the details here:
https://www.flyertalk.com/forum/showpost.php?p=29681218&postcount=45)