I observed that when enabling backends locally, the SDK tries to load and reserve memory compatible with you configuration file. For instance, if you have a B4 configured backend, then the SDK starts a new VM thread with all that memory and this slows down the whole development cicle.
We have added to our build script (we use ant build.xml), a target to enable / disable backends, by having a backends.in.xml template, and using ant filtering. This is awkward, but solved the problem of running the local SDK without the need to test backends locally.
Hope this helps,