Compressing and encrypting large files needs to be done on the device before a report can be sent. The time it takes to perform the compression is, in large part, a factor of how powerful the device is. In general, the older the device, the slower it is to compress. If you are finding it is taking too long, it might be time to upgrade your device!
The best iOS device will always be the newest! At this time the iPhone 7 Plus is the top of the line. The Google Pixel is the best Android device we have come across for use with PicSafe.