@vinny55 There are lots of professional R2R machines with 15 IPS. The thong about professional machines is that they are built like tanks and calibration and line up is easy to do; after all a decent tape tech would line up the machine every day in a studio, back in the heyday of tape. Having had a couple of domestic machines (Revox A77 and a high speed G36), I wouldn't go back to one now.
Checking the repro head azimuth on a tape is probably the most important part of line up, as the high frequency losses are significant, is the repro head is not aligned correctly to the way that the record head was aligned when the tape was made. This is something that most people don't worry about on a domestic recorder with commercial 3.75 and 7.5 IPS 4 track tapes. But that's another story.
Checking the repro head azimuth on a tape is probably the most important part of line up, as the high frequency losses are significant, is the repro head is not aligned correctly to the way that the record head was aligned when the tape was made. This is something that most people don't worry about on a domestic recorder with commercial 3.75 and 7.5 IPS 4 track tapes. But that's another story.