The Speedtest app from Ookla has long been able to tell you how fast your internet connection is, but now it can tell you how fast individual apps are. The feature is called Speedtest Live, and it's available in the latest version of the Speedtest app. Be warned; there are some potential privacy concerns.
Speedtest Live is tucked away inside the tools menu of the Speedtest app. When enabled, it uses a VPN on your device to log the data usage by each app on your phone. You get a list of apps along with their average up/down speeds, ping, how much data they've used, and more.
You should generally be wary of leaving a VPN running unless you trust it completely—free VPNs have been caught selling sensitive user data in the past. There's no reason to think Ookla is doing that, but I would not be surprised if it has plans for all that app performance data. Even if you're the paranoid sort, Speedtest Live could be a good way to troubleshoot app problems. The app update is live in the Play Store, and we've got it on APK Mirror.