How can I generate iOS screenshots without using a simulator? I'm not too far off from releasing my first Cordova-based iOS / Android app. The final step is to upload screenshots of my app in various resolutions (e.g. one to show how it looks on iPhone 6 Plus, one for iPhone 4 etc.).

I have an iPhone 4, and a 2009 Macbook with 2gb of RAM in it (both second hand from eBay. I just needed the bare minimum for development purposes), so running a simulator is painfully slow and takes a long time to do most things

Is there a quick and easy way to prepare the 20 or so screenshots I need without having to own or get access to various sized iPhones, or struggle through the simulator? I'm looking for something I can use fairly often as I release new versions so I don't have to struggle every time.
A popular solution to this problem is  this  automation tool called snapshot. It is apart of a suite of tools made to automate iOS and Android developments. 

For relatively small applications though, the simulator isn't too bad.