It doesn't seems like too much, but you could trim it down in many ways.
Usual ways in opamps is to trim both 1k5 resistor, R82 and R87 if I'm reading right. In some power amps it's used a DC servo, but I think it's overkill for your case. Other option would be to add a bias to Q15 base, connecting a trimpot to C48 + side, maybe you want to limit the range putting a trim pot between two bigger resistors, maybe 1k trimpot and two 10k resistors, for a controlled range, maybe less than that is needed to cancel out your level.
Remember the DC will drift with temperature, if you want a better idea of what's happening connect a dummy load and run some signal to get a working temperature, then read the value again so you know how much is drifting, if it goes crazy (which I won't expect) there may be a problem somewhere, you could find it or add a DC servo, which would correct it all the time. In any case 70mV is pretty low I guess, shouldn't harm a speaker, it would probably have ~6Ω of DCR, so it's about 12mA and less than 1mW, hardly a problem.
JS