Miniset training. This partial dataset should somewhat reflect the mean/distribution of your actual dataset. Also, if it is very small, validation set should be a little larger.

For learning rate tune a “base learning rate” and scale it to your desired batch size using sqrt_k or linear_k rule. https://stackoverflow.com/questions/53033556/how-should-the-learning-rate-change-as-the-batch-size-change. Personally, sqrt_k rule works very well, but linear_k works too (depending on problem/model)