It could be a number of things
What's your average FPS?
Seeing as though you are playing on integrated graphics, make sure you keep your Graphics Drivers up-to-date (
Intel Drivers Page)
What do you have open at the time?
Can your laptop run other games better?
Some users find that upgrading to Windows 10 fixes most issues that halo 2 has
(Not to mention a new Direct-X version)