I don’t know where drive is located and how it’s mounted to the system, but in case it’s a network mount your current script performance would most likely be limited by the data loading speed from the network.
I don’t know, if Colab allows you to store data locally, but as a quick check you could replace the DataLoader with random tensors and check the training speed again.
If the usage of the random tensors accelerates the speed significantly, it would indeed point to a data loading bottleneck.