Yes, you will lost your App, especially the WhatsApp messages.
But good news is you can easily transfer other data. If your iPhone is brand new, the first choice is install the "Move to iOS" in your Android device, and in your iPhone you will see the option of "Move data from Android" in the set up screen, then begin you transfer of contacts, messages, photos, camera roll to iOS.
Besides,Google Drive, Google calendar and Gmail are avaliable in iOS, so you can sync your documents, calendar, etc.
If you need a convenient way, try this to
transfer data from Android to iPhone.