If you look up "Creating an Indexed View" in Books Online, you'll see that there are a lot of restrictions on what types of views can be indexed. In particular, you can't index your view if it contains any of these elements:
SUM functions that reference nullable expressions
If your view is as complex as you say it is, there is a good chance that it cannot be indexed. Also, when you index a view SQL Server creates a permanent virtual table with the results of that view, and which is then updated any time any of the values in the underlying tables are updates. This can slow down other processing.
I think you would be better off rewriting your statement as a stored procedure rather than as a view. Stored procedures are more efficient than views.
Also, post your code and we may be able to find ways to make it more efficient.