If you have created a pattern which seems to be slowing your system down considerably, try enabling the option “Geometry Pattern” from the pattern property manager. It may not work for all types of patterns but it can make a significant difference on many.
You can check the performance of your part by going to tools, feature statistics. It will tell you the rebuild time of your part's features. Check the rebuild time on the pattern before and after enabling the "Geometry Pattern" option.