Hi xplanescientist, the 39FPS was using the 37-class SSD-Mobilenet-v2 model trained on the PETS dataset (see this post).
The SSD-Mobilenet and SSD-Inception models from Hello AI World are using the 90-class COCO dataset, so performance is lower with more classes. You should be able to get around ~22FPS for the network processing with SSD-Mobilenet-v2 (COCO) on Nano. Eventually, if you were to retrain your own SSD-Mobilenet model with TensorFlow and fewer classes, you could improve the performance by only training for the classes you needed.