The first time you deploy an app, Mendix will need to setup the environment. If you’re running in a sandbox even more so. My guess would this is down to the fact it is a first time deployment.
Also, if you are running in sandbox, Mendix shuts down the app if it is not used. This means whenever you start using it, Mendix will first have to start the app again, which also takes a noticeable amount of time.