first IUI questions!

Hey everyone! So my husband and I are in the process of hopefully getting our first IUI next weekend. My doctor told me that we have a 15% chance of it working. My question is- is that 15% on top of the 33% you have naturally just with ovulation? May be a stupid question but I just thought of it while logging in glow. ALSO- if you have any tips for a "first-timer" I would love to hear it!