There is an usual issue that opening site can be time-consuming for the first user accessing it after IIS is recycled. But there is an option how to have warmed up site at any time. There are some features starting from IIS 8.
What we need to do:
1) Go to site application pool settings and change Start Mode to "AlwaysRunning"
2) Go to site settings and set Preload Enabled to "True"
The first thing makes application pool running just after IIS is recycled, the second makes warm up first call to the site.
For additional information you can take a look at:
