I have received the fabulous Testament remastering of Keilberth's The Ring CD set. There is also a 19 LP stereo set produced by the same company but I wonder if there were ever 15 ips tape sets commercially available.

Welcome to TC, Horacio!

The CD set you bought isn't a "remastering" - it's the first release of the original recording, which was presumably recorded on tape. For a variety of reasons, it sat in Decca's vaults for 50 years before Testament issued it on CD, and later on LP. I'm pretty certain that it has never been issued commercially in any tape format. Perhaps an illegal copy might have surfaced on tape at some point, but it would have been far from high quality.

 

The main reason it sat in the vaults was that Decca was planning for the Solti Ring in the 60's and was afraid the younger voices in Keilberth would upstage Solti.

 

Varnay is epic in this recording. I think she is the best of anyone in the Dawn Duet. She is in really good voice still in this recording.

 

I agree. She might actually be my favourite Brunnhilde.