If you want to stay on iOS 8.4 take care that you do not accidentally update to iOS 8.4.1 because you won't be able to get back to iOS 8.4. If you do update you will not be able to jailbreak your device. Pangu Team just demonstrated a jailbreak of iOS 8.4.1 but it's likely that won't be released in anticipation of iOS 9.
You may want to save the SHSH Blobs off your device if you haven't already.
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