How do I speed up my apps opening time?

When I select an app on my iPhone 6, a splash screen appears while the app loads. It takes so long for the Ring Doorbell app to load, the person at the door has left. In all fairness, I have the same long delay no matter which app I select. The Ring Door app is the one which is causing problems. The whole point in have the doorbell is to be able to answer the door using your smart phone when you aren't home or indisposed. Any suggestions how to speed up the load time for my apps?

I recently upgraded my wireless router. I have an average download speed or 90-100 mbps, a download speed of 10-12 mbps and a ping of 23 ms. It more than meets the minimal requirements. The problem seems to be with the slow loading speed of the apps on my iPnone 6. Thank you.