Hi, I've got a problem concernbing the sped of my application. Is their a easy way to find the spot which causes the speed drop down?

I'm just drawing lines on a picturebox. When using only lines i could come to a speed of 1:10. Now I'm using the API POLYLINE (there are about 3600 lines) and the speed dropped down to 1:6 why? The only new things are the API and the change of some variables to LONG instead of SINGLE. The speed drops down even if the API isn't realy used?