I have learned a neat trick how to make Inventor parts (IPT) smaller and faster to load. You probably know the red cross marker “End of part” (EOP) displayed in the model tree (model browser). You can drag this marker with your mouse and drop it at the very top of the tree. Now save your model.
All the modelling features will be grayed out and your model will be initially not displayed in assemblies. The IPT file size will be much smaller, there will be no preview stored in the file and this file will load much faster (consuming less memory).