While there is no limitation to the number of feature classes you can have in a geometric network, every feature class you have in the network comes with a cost.
Each time a feature is created, the geometric network has to search through each class and determine if there are any coincident features. So, the more feature classes you have in the network, the more time it takes to search for any coincident features. The object loader is essentially a batch loader that automates the loading of features; but it still has to create them one at a time.
I'd suggest that you look at ways of decreasing the number of feature classes in your network by combining several feature classes into 1 and using subtypes. You can also look at eliminating any feature classes that aren't being used at this time, if you've added empty feature classes to the network thinking you'll use them at some point in the future, remove them and only add them when needed.
you best option is probably to delete the geometric network, get all your data loaded and then recreate it. It will no doubt be much faster.
You never responded with how many features you are loading into the network. Can you respond with that?