R - GBM | Data making trained GBM model very heavy

We are using GBM model to train on really voluminous data ~15GB. The trained model size becomes huge ~17GB. In the trained model we see data saved along with trees and other model details, taking around 96% of total model size.

Is there any use of data in trained model, specifically for prediction purpose. We are saving the model and reloading the model while prediction, which is taking a very long time.