Yes, there is a possibility. In some cases using QoS out of the box doesn't work well for some platforms. We have to either configure it to work correctly, i.e. gaming is a best example. Or turn it off. I generally have users turn it off if there not doing any high bandwidth applications like gaming or torrents. Streaming is good however if your streaming video and someone is surfing, gaming or streaming something else, it can produce lag and buffing on the video device. In most cases, people are watching video or only doing one thing at a time with the router services. So QoS can be turned off. However if you seem to have multiple devices online and using router services, it's recommended to use QoS to ensure that everyone is getting equal bandwidth and internet.
Host ISP, Router and additional APs need to be properly configured to effect good performance. Any one of these and other external conditions can impact performance.