You are not running your engine hard enough. If you want to reduce the frequency of your regens, you have to run it at higher rpms. 1500 rpms won't cut it. I understand what you mean about not needing more rpms for the task your working on, but the emissions system needs more rpms to run cleaner and run the filter hotter. The hotter (within reason) your filter gets, the less often it will regen.
I no longer have any concerns on my own system (different design than yours) because mine is completely removed. Now I can operate at whatever rpm I think is required to perform the task at hand, and to hang with all the emissions B.S. You have my sympathy.