it appears that all or almost all of those 15-35m ppl had prudish values?

So, first of all, on this - I have a previous answer that addresses this perception: Why are people today fascinated with the Victorian era?

"Victorian" has come to mean a lot of things beyond "relating to the reign of Victoria, 1837-1901": broadly speaking, things that are recognizably not "modern", the way that we see ourselves or would like to be seen. This started relatively soon after the end of the queen's reign, with those in the late 1910s and 1920s seeing themselves as part of a "post-Victorian" age that was starkly different from what had come before. This has largely been studied in the context of early twentieth century writers like those of the Bloomsbury Group - Virginia Woolf, Vita Sackville-West, T. S. Eliot, et al. - who distinguished themselves or who were distinguished by others as being intentionally anti-Victorian, or whose pro-Victorian sentiments need to be examined beyond simply being considered conservatism. These writers generally came of age around the turn of the century, spent their childhoods in middle- or upper-class Victorian households, and went on to become an educated, elite group that conspicuously spurned the mores and standards of their parents' generation, which to them represented the whole of the Victorian era despite being a highly skewed view of the entire period and all of the people in it.

The people of Victorian Britain were far from prudish, on the whole. The upper and middle classes had standards of etiquette that were in some ways more strict than ours, but they knew about the existence of bodies and swear words and such.

Women's formal evening dress had been more revealing than day dress from about 1815, at which point it became something of a rule (though not hard-and-fast) that women would generally wear long sleeves and cover their torsos up to the neck, unless they were affluent enough to have formal dress, which would have a somewhat wider neckline and short sleeves. For instance, evening dress, day dress. By the 1850s, as the sleeve-to-shoulder seam dropped lower on the arm, evening bodices were quite open at the top, and the sleeves were quite short; this kept on as the pattern for evening dress until the 1880s, when the armscye seam was fully back on the shoulder and evening dress essentially had straps.

The basic idea behind more revealing evening dress was that these parts of the body that were understood to be attractive but not appropriate to show to all and sundry - the shoulder, the upper chest, the arm. Outside of wealthy circles at dinner or a ball, showing them singled you out as disreputable, but if you could afford a very expensive silk gown and had invitations to fancy parties, it was not only acceptable but expected.