Personally, I don't have this problem with any of my new smartphone especially when it comes to typing. I make use of Microsoft SwiftKey Keyboard. I have an account with them and all my keystrokes have been saved. Whenever I get a new, I will download the same Microsoft SwiftKey Keyboard and login my account. It would be just like my old phone.If your iphone is lagging, I will suggest that you free up some files on it. That could be part of the reason the device is not giving you what you want. What do you think about that? Again, when you start working or writing on a new device, it is going to take time before you can be able to master working on that particular device too. So, be patient with it.