Hello. Yes, it can be pretty common for other wireless users to experience slower performance if one user is doing large file transfers. One way to combat that can be to implement Airtime Fairness on the APs, though it's only available on v6.0+ code and not something I've yet tested.
Remember that wireless is SHARED airspace. Each wireless client is competing for a slice of the pie, in general terms. The more clients you have in that airspace, and the more network traffic they generate, the harder it becomes for everyone else to get a slice of that same airspace.
One other thing that I have seen cause HUGE problems in some wireless environments is co-channel interferences and also outdated/old wireless drivers used on the wireless devices themselves. I've personally run into several instances where having 30 laptops on an AP will cause severe performance problems, 1000ms-3000ms ping times and dropped packets, etc. yet those same problems being totally fixed merely by updating the wireless driver used on those same laptops.
Truth be told, in the past, HP MSM wireless also had their share of problems with performance back in the 5.7.0.x firmware code days, but newer releases have been FAR better and much more reliable when it comes to wlan performance.
Last, excessive broadcasts will absolutely ruin your wireless airspace as well, so I always recommend to ENABLED broadcast filtering at the VSC level, both for guest wireless and secured wireless VSCs.