I experienced the same behavior on my phone as well, and I fixed it simply by turning off and uninstall apps that I didn't need. This lag was caused by performance spikes when other applications were running in the background. Long press the menu or the task switch button next to menu button (usually on the right) and then close all the applications. Launch Snapchat and continue to enjoy its features. This is not a bug or something related.
Additionally, you can upgrade the phone to a more powerful model.
