You can just always postpone an update so that you'll be stuck in whatever update you are in. You can also disable Autodownload Over Wifi so that you'll have the control of what updates you want to download.
Though I recommend you still update because Security Patches makes your device more secure. If you're experiencing slower performance after an update, try sending your concern here in Samsung Members. You can also start clean by factory reseting your device as a temporary fix if it solves your problem.
Hey there! Amazing afternoon! We do suggest you to still do updates on your device, as this still provides extra security on your phone, and keeps compatibility issues at bay. You may do so as with what your fellow member suggests, by starting clean and resetting your device. Stopping updates may bring you closer to what you're fearing of having such performance slow down, and may further induce compatibility issues with other applications. Also, in the long-run, as you encounter compatibility issues and decided to push through "again" with the updates, it would even slow you down since you'll be catching up on more and more updates, rather than installing just the latest one. Hope to enlighten you on this one. 😉
