The node runner application used by SharePoint 2013 preview for search related process slows down the system due to memory leak issues.
To fix this issue follow the below 2 steps
1. Open SharePoint PowerShell window and execute the below command
Set-SPEnterpriseSearchService -PerformanceLevel Reduced
2. Open the config file at C:\Program Files\Microsoft Office Servers\15.0\Search\Runtime\1.0\noderunner.exe.config and change the value of memoryLimitMegabytes in node to some other value other than 0, say 100 or 200 which sets the cap limit for memory to be used.
Restart the machine or service which ever you find easy :-)
Check out this technet link for more info..