Three MAJOR reasons the Hero runs slowly -
1. This probably applies here - Android 1.5 has a serious bug in the location services. If more than one application uses it, it duplicates the processes running, and these duplicates never close. Example -
Maps is running and using location.
@ Noon, HTC location tries to update your clock and weather.
Android suddenly takes those two processes that need location, and turns them into four. And they never quit.
3 hours later, when HTC tries to refresh the weather, it turns into eight.
Then sixteen, thirty two, and so on until the processor finally becomes so bogged down it starts to affect performance.
To fix it, disable all location (GPS, Network and wifi) then re-enable. Or reboot the phone. Do it once a day and you won't be affected too much. This affects every 1.5 user, but folks using sense see it twice as fast. It was fixed in 1.6
2. Sense framework depends on more free RAM. The sense framework is actually much faster than stock Android, but only if it has enough empty RAM to do it's job. That threshold is somewhere around 35-40 MB free. Anything lower than that, and it can't buffer in RAM correctly, will try to use the SD card (Rosie Scroll folder) and perform poorly. Big problem when the next issue is considered
3. Android is still using memory management designed for old software and old phones. It has never been changed since it was written in 2008. The way it stands now, it will only try to maintain 20 MB free while the system is in use. Rooted phones can get around this, then the problem disappears, and Sense is amazingly fast as long as you remember to toggle your location on and off once a day. This WAS NOT fixed in 2.1 on any current Android device.
Holler at me if you decide to root your phone and try to correct these. I can help