Just for kicks go to Tools--> Manage Add-Ons. Then sort by the LOAD TIME field. This will show you if any add-ons are cause extended time for tab opening. If any have a load time of a couple seconds or more disable them and restart IE. If this helps try uninstalling or updating any problem add-ons and see if there is any improvement.
If that does not yield any results try opening IE in No Add Ons Mode. This will disable anything that not a core IE component, if it still happens try an Antivirus/Antispyware scan. Malwarebytes is good for Spyware/Adware.
My last recomendation would be to go to Tools-->Internet Options-->Advanced-->Reset. This will reset all custom settings to IE.