Do you have original bjts installed?
Looks like you need some fine tuning in the bias generator ckt (H715) to increase the voltage drop across H706,707 collectors. The Vbe multiplier voltage drop is controlled by the current generated by the bias network connected to H706,707. Changing any comps will affect it.
See if changing R470 to a 2K multiturn pot will provide enough bias to meet spec, you want around ~30mA of bias in the o/p bjts. you have 0.22ohm emitter R's so that is 6.6mV across each R or 13.2mV across both, spec is 15mV as you mentioned.
Make sure the bias pot is at minimum setting to start with and always a good idea to power up on dbt when you are doing this fiddling until you get it where you want.