Good Evening, Barry,
Given the conditions described immediately above and without seeing the actual negative, I don't find the exposure time to be particularly unusual. My exposures from 4 x 5 with a condenser-head Beseler MCR-X are not too much different for typical 8 x 10 prints. Why be concerned about using ƒ11 or ƒ16? With LF (especially) or MF and a high-quality lens, I think you'd be hard-pressed to detect any difference in image quality whether you use ƒ8 or ƒ16. Most of my 8 x 10 prints from MF negatives are made at ƒ11; most from 4 x 5 are at ƒ16. The overall negative quality seems more important to me in most cases.