I have written a website in Angular 2. Now I want to create a app out of this code because I would like the website to run faster on smartphones and so I tought that if I put it into a app most files would not have to be downloaded every time the page is visited. Is this a good idea to speed the app up and has anyone suggestions?
PS: I know Ionic and I've already used it but I dont want to rewrite the app with ionic, instead take the existing code and build the app out of it.
I think you should look into Apache Cordova. This is what ionic uses to access the native functionality of the device. here is a link for the site You can use any form of js, css, or html. it also has plugins you can use. Go though the Get Started button and then start the tutorial should help you out.
Speed will depend on how many ajax calls you make and the logic you use to create the app functionality. Having the website stored on device will speed up the initial load of the js, css, and html. But if you have good internet speed and not much to load the speed up will not be noticeable.
I think the real advantage of having a native app (even through Cordova) is that you will have native access to the device file system and functionality that you would not have with a website. Check out the plugins for Cordova. Push notification, camera or any number of other plugins...