Addition times from 1' to 15' are possible for this emulsion, but difficult o do by hand. The contrast will be quite low at 15' if everything behaves as normal, and the speed will probably move about 1 stop, but it may appear to slow down due to the loss in contrast. Here is a typical curve of the usual senitometric change with addition times from 8 - 14 minutes with a given emulsion. You can see what happens to speed and density as well as contrast.

PE