Assume that you use Microsoft SQL Server 2012 Analysis Services (SSAS 2012) or SSAS 2014 in Tabular model. When you perform a full process on the model multiple times, it takes more and more time to complete than the initial processing.
The issue was first fixed in the following cumulative update of SQL Server.
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server: