Doesn't sound like a great report.
As JAE noted, it is an opinion not a guarantee or warranty. I gather from your handle you are in Canada. BAretired, dik or ajk1 can give better advice on the legal ramifications to a P.Eng. than those of us who practice in the US or other locations.
Having said that, I'm not shy about offering my $0.02 worth....
Most jurisdictions in the US and Canada put limitations on how long an engineer's liability can last for DESIGN services. Most do not address the limitation on one's reliance on statements or opinions made by an engineer. In the absence of further directive from a statutory source or legal precedent, the engineer possibly defined his own time limitation with the 15 years comment. That's a long time to be liable for something as fickle as a construction material.
I agree with Mike...wouldn't buy a structure with a wood foundation and wouldn't recommend it either.
Further, even with disclosure, inspection, structural warranties and the like, a real estate purchase is effectively "caveat emptor"!