I'm not sure if this would help
1. Extract the raw data from your data source and store them as qvd's
2. Do the transformation by loading extracted qvd and store them as transform qvd's
3. Load all your tables into one QVF file, which will be your Data Model file.
4. Use your Data Model qvf file as Binary Load and do your designing in source file.
5. Store big/complex expressions in variables.
QVD's load faster and decrease the size of the file and it's better if they are optimized qvds.
If it is still taking time to load then check with De bug mode available in your script to know where exactly it is taking time? It can also be due to number of rows you have in your data set.