With our team, we also found shared folders performance to be too low. Our Python framework/app is very read-heavy and stat() a lot of files (the Python module loading system isn't your friend)

We ended up using the synchronization feature in PyCharm to continually rsync files from native FS into the VirtualBox instance. Huge perf improvement but a little more cumbersome for the developers. But so far it has been working good, PyCharm's sync feature does what it is supposed to.