I have not tried this myself, but somebody at Android Central forums claims that you can install the 1.5 MR2 update over the 2.1 OTA update after upgrading from 1.5.
See this post/thread.
(The "above procedure" was this:
Again, I have not tried it myself, and really do not wish to, but for those who want 1.5 and use the known root procedure from there, perhaps it's worth a try?
See this post/thread.
Just tested the above procedure with the OTA version of Android 2.1, and the firmware installer above works like a charm. I'm back at firmware 1.5 and am able to flash new firmware (and more importantly, I'm able to load rootable firmware again). I'm going to post a how-to guide here and at XDA forums when I finish, so that others can follow my lead.
(The "above procedure" was this:
Download the MR2 Uprade Eris ROM from verizon partner:
Personal Communications Devices
(or, you can download the file directly - ADR6200_MR2_Upgrade.zip)
1. Unzip the file
2. Plug your phone to your PC/MAC.
3. Find your folder (MAC or PC folder)
4. Run .exe file in the folder "RUU_Desire_C_Verizon_WWE_1.17.605.1_release_s igne d_with_driver.exe"
5. follow on screen instructions.
Again, I have not tried it myself, and really do not wish to, but for those who want 1.5 and use the known root procedure from there, perhaps it's worth a try?