Since people are still talking about re-indexing and not reading posts in the thread.No issues on my 7 Plus. Apps open snappy with no lag whatsoever.
Re-indexing is one thing, but photo analysis (facial, object recognition), conversion to HEIF, and uploading photos to iCloud when you have optimisation on can also lead to lag, battery running down faster and phone running hot. Depending on the size of your library, this could take a long time.