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Yes, it's still pretty fast. I haven't tried playing games or taking video with it though, but it's fine for texts/calls/etc.
 
Is it because of the 2 GB of ram ?
Yup. Still on my launch 6S, and it survives even the buggiest iOS 11. And performance is not the issue. It’s the battery that its Achilles heels. Mine is now on a battery case as I depleted the battery to almost half by noon (and this is after replacing its battery twice). Buy performance is perfectly fine. Apps run just fine.

I’m glad Apple now puts larger batteries in the latest iPhones. We know the SoC will be fine for 5 years and plus, battery life becomes the bottleneck.
 
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