I've found this developer quite interesting in brief tests. I decided to give it a try after becoming a great fan of Crawley's FX-37 for T-grain films and wanted to see what his work offered for traditional emulsions.
FX-15 has great midtone gradation and better highlight detail than D-76. The times I'm getting for FX-15 are comparable to D-76 1:1. I need to do some side-by-side comparisons with Xtol next, but my guess is slightly sharper with a slight increase in graininess -- a nice compromise point between a high acutance developer and a more mushy solvent developer. If you use Xtol 1:1 or higher I doubt the differences would be important to you. But if, like me, you enjoy the alchemy of chemical mixing then this one seems a gem.
Start times for FX-15 1:1 @ 68F with three agitation cycles every 30 seconds:
Foma 100 (Arista.edu Ultra) 10 min.
Efke 100 10 min.
Agfa APX 100 12 min.
Since times are tough to find I'll add more here as I get them, and send them to Digital Truth for the dev chart.