Databse Restore is very slow

Hi,

I was trying to restore the database which usually took 50 minitues maximum, but since last couple of days it is taking more than 2 hours

In Activity monitor I see BACKUPTHREAD & BACKUPIO with status as suspended.  In locks by object area of activity monitor, I see sew lines on tempdb database with subtype as DATA_SPACE, INDEXSTATS, request mode Sch-S & Sch-M

SQL Server Logs show "cachestore flush for 'Bound Trees', 'Sql Plans' and 'Object Plans'... lines when restore process started.

Can anyone explain the reason ,solution and where i can more information about it ?

Thanks in Advance.