Experimental research on positive-pion photoproduction on the oxygen nucleus in the 16O(γ, π+p) reaction at high recoil momenta of the residual nuclear system was performed. The yield for the 16O(γ, π+p) reaction was analyzed using a model that takes Δ-isobar configurations in nuclei ground states into account, together with the earlier-measured yield of the12C(γ, π+p) reaction. The estimated number of isobars per nucleon NΔ = 0.012 ± 0.005 was obtained for the 12C nucleus, and 16O NΔ = 0.018 ± 0.004 was obtained for the 16O nucleus.