Whether or not a network is secured would have no effect on network management and throttling. Security on a wifi network limits the ability of users to connect to the network, it does not be default and not without other features prevent network administrators from filtering or viewing traffic (in most cases if you are using end to end encryption (e.g., HTTPS) they cannot see the content).
There are a few things to consider in terms of performance on a wireless network. Yes, it entirely possible the network admin or network management tools automatically throttle traffic. It is more likely though that this is a result of network activity. The more data and individual connection you make the more likely there will be collisions in the air and retransmissions. You might be having poor connectivity on the other system, but if you are not doing transfer intensive activity you may think "this website is just slow" or maybe the website is designed to load the images you see first preferentially before those that are not initially visible.
The cost of equipment and management make it unlikely the admin is doing any type of class of service or other filtering of certain types of traffic.
You could put all of your traffic over a VPN, tor, or something else to encrypt it, however, the encryption will add extra overhead which will likely yield inferior performance.