The raw numbers say 26 wpc in a "normal" sized room should generate up to about 105 dB (which is generally accepted peaks of classical/jazz, rock is 110 dB) with the M3. Most audiophiles I know do critical listening at 85 dB (less for casual listening).
But with two 15 inch drivers having a beefy power supply is also important and as a vintage piece I assume you'd be covered on that count.
