The 25 seconds sounds like a lot, but could be affected by:
- Slow server (we have one very popular Russian mail service that has been slow for the last month or so, taking up to 40 seconds to connect, 20 seconds to select a folder, etc.)
- The device's network connection (mobile has higher latency than WiFi, no matter what its speed is... except LTE)
- The "messages per page" setting in AquaMail.
This last one is how many recent messages the app looks at, every time it checks mail. The default is 25, but it can be set in the thousands range. Obviously, that's much slower.
That's about all I have to say without a debug log in front of me. My telepathic skills are limited