The PS4 and Xbox may have difficulty running resource intensive content like Mutant Survival. We have released updates to improve the performance on consoles. Unfortunately, many of the performance issues are out of our control and depends on the version of the Minecraft running.
We know that Mojang continually updates the clients on consoles to improve performance. Most players don't have these problems - so we don't know why some do. So while it may not work for you today, it may start working noticeably better in an update to Minecraft in the near future.
If you also play Minecraft on other platforms like Windows 10, please be aware that your purchase on PS4, Xbox or any platform also entitles you to download purchases on other Minecraft Bedrock platforms. Just make sure to use the same Microsoft/Xbox Live account as the one you purchased content on.
If the latest updates does not perform to your satisfaction, you can contact Mojang or the app store to request a refund or report the issue.