На iPhone 7 новая система работает быстро, но на старых устройствах могут наблюдаться проблемы с производительностью.
To download the update, head over to beta.apple.com/profile to download the configuration profile for your device. Once you install that, you will be asked to restart your iOS device. After the device restarts, head over to Settings > General > Software Update and you will see the public beta as an update just as you would any other iOS update.
We installed the update on one of our devices and noticed some minor bugs and glitches in the interface, which makes it perfectly clear that it is nowhere near ready to install on your primary device. The performance is snappy but we did install the update on a speedy iPhone 7 and it's likely the performance won't be as good on older devices.
So, the old adage still stands. If you have a spare device that's not too old then by all means go ahead and install the update. But it's not worth downloading this on your main device right now and it is highly recommended you wait for the final version to release sometime in September.