Dear Tariq,
1) I think you are using the Universe directly on Multi provider. The issue would be with the your first cube which has 200 keyfigures and 50 characteristics. Is there any way to reduce the size of this. Is all the fields used in the dashboard. If you reduce size you will certainly benefit on performance.
2) If you create one query for brining in the 2 years data together that will also help.
3) Split up for all the cubes is not required as the data in other infocubes are very less. Make sure that first cube is consistent in SAP_INFOCUBE_DESIGN, aggregates are getting used when you execute the dashboard.
4) Please find a link for improving the universe performance , which also can help you.
http://scn.sap.com/community/semantic-layer/blog/2014/05/14/universe-optimization-techniques
Regards
Gajesh