That highly depends on the model and the textures as well as the target platform. My old Galaxy with 1.6 has 16mb VM memory, my Nexus S with 4. 0 has 48mb available.What's the polygon count of your models and the size of your textures?Some hints: http://www.jpct.net/wiki/index.php/Reducing_memory_usage
I am wonder if it is possible to use JNI to allocate C memory for use by jPCT or OpenglES call ? the native code will not limit by VM.