Performance issue and errors when more then 170 request each minute

Hi,

We have a Windows Server 2012 and IIS 8

I've serious problem with a a webservice that is printing labels for European warehouses.

Sometimes we have to print more then 170 labels each minute.  But it becomes extremely slow and i find the following messages in the log

200 0 0 3140

200 0 64 74829

200 0 64 86641

200 0 64 114204

200 0 64 60063

200 0 0 3546

200 0 64 108704

200 0 64 144189

200 0 0 3500

200 0 64 98267

200 0 64 65188

200 0 0 4562

200 0 64 98485

200 0 64 89141

200 0 64 139017

200 0 0 5484

200 0 0 5187

200 0 64 80001

200 0 64 100142

200 0 64 142564

200 0 0 3890

200 0 64 126501

200 0 0 4000

200 0 64 122126

200 0 64 62829

I've no experience to fine tune the webserver but still have to do it. What should I do?