I have DJI's 15mm lens. Recently a friend of mine bought the Inspire 2. I'm wondering if I could borrow his 24mm Olympus for use on my Inspire 1 Pro.

Yes, it will fit, but make sure you balance the camera.
If it already has a balance ring, you're good. If not, it may take a stack of 2 or 3 filters as that is a lighter lens than the DJI 15mm.

Are you sure it is 24mm Olympus? Sorry that it is not in our compatible list of Inspire Pro, so does the Inspire 2. We don't suggets to mount other lens which is not in our compatible list to protect the gimbal and guarantee the footage quality.

what would i need to balance the Olympus ED 45mm and the ED 14-42mm lens?