That could be it. Here’s a way to test: log in to Zwift and then turn off your internet connection (WiFi, what have you). All the other riders will disappear but you should still be in game (but nothing will save properly).
Ride around a little bit and see if the frame-rates are still choppy. If so? Then perhaps there’s a driver issue or your laptop is using the built-in graphics chip rather than the GTX 950M.