Which Pega version are you using?  IE11 is known to be the worst performing browser so I am not suprised when I hear that IE11 is performing worse than other more modern browsers like Chrome, Firefox and Edge.

Please see the below article for more information.  I have pasted some relevant parts below.

Pega Platform Client Operating System and Browser Support

Microsoft Internet Explorer 11 performs the worst among all the supported browsers.  Other browsers have innovated heavily over the last few years, while Internet Explorer 11 is purely in maintenance mode.  It uses an old and proprietary rendering engine, runs as a single process on the operating system, and has suboptimal memory management.  We do continue to support Internet Explorer 11, as many of our customers have standardized on IE11 due to other legacy software that only works on Internet Explorer 11 and prior versions of Internet Explorer. 

For Pega Infinity, we recommend that our customers move away from Internet Explorer 11 in favor of using Chrome, Firefox, or Edge on Windows, to get the best performance from their Pega applications.