25mm seems the most useful in an inner old-town environment. Just as an example, I traveled to Spain, staying near Malaga and visiting Granada, Seville, Marbella, Ronda, and Tangier. We had a rental Fiat so traveled around the area. I took a CLE and Bessa-L with 15mm, 25mm, 40mm, and 90mm. The 90 was used once. The 40mm was used a few times. Finally, I settled the 15mm on the Bessa and the 25 on the CLE as those were the two more-used lenses, and especially the 25. In the narrow streets and building interiors I felt I needed context.