As a general comment (even if the original poster knows this well):
As far as I know 8015 is the property of the SAE and is available from them only by purchasing it. But I sure like to be able to know the standards by which my equipment may be certified.
Also useful for those interested in certification, is to check out PIA's proposed TS-135 available from their web site.
As a clarification, PIA TS 135 is not proposed. It is a final PIA document. It has been submitted to the FAA for consideration as the next testing reference standard for TSO C23. So the TSO change is proposed, not the PIA document. Wether the FAA adopts it or not, the PIA document exists.
SAE is no longer interested in supporting this TSO with a standard, although theirs is still the current standard. That's why PIA has written one.
I doubt it as the last that I knew the FAA lost it and it has not been resubmitted yet. Since it has to be resubmitted it is being gone over again to make corrections that were found after it was sent the first time.