Hi Mehrtash,
The legacy ADVI have not changed between 3.1 and 3.2, so I wouldn’t expect any change of performance.
As for the slowdown of ADVI implementation between 3.1 and 3.2, it is quite likely as the new framework is more flexible but also computationally more intensive. This is related to some of the theano bottleneck @ferrine faces when he is implementing the group approximation, so it is likely quite difficult to improve from our end.